I picked up some point & click adventure games such as the King's Quest series during the summer sale. I don't usually play them anymore, though I used to when I was a kid. Thought I'd go back to the genre for something different. I remember I could be really bad at puzzle solving, and I'd have to frequently go to walkthroughs to figure out how to get past certain obstacles.

My question is, do you have any general strategies, (no adventure game in particular), that you use to help you get through the game's challenges, without needing to resort to walkthroughs?

try EVERYTHING

By that I mean, I don't why the hell putting a trumpet onto a tree would accomplish anything, but at some point you are going to play a P&C and something stupid like that is going to be a solution.

-Combine the doughnut with the salamander and use it to unlock the door.
-Oh yeah, duh, why didn't I think of that? :P

I fear you can't really avoid getting stuck by applying a specific strategy, it really depends on how good the game design is, and many P&C adventures are occasionally lacking in that department.

However, when I play P&C adventures, the most basic strategy is to scan every room your in, examine any hotspot you can interact with, pick up everything that isn't nailed down, talk to everyone, exhaust all the options before moving onto the next room. Don't just run around from one room to the next, thinking you can always come back and examine it later (you probably can, but this method is inefficient and makes you prone to overlook something due to impatience and repetition, it may cause you to run around in circles soon).

As a sidenote, old Sierra adventures like the King's Quest series are not the easiest to get into, I think in one or more of the earlier ones you can even get into a dead end. In any case, for the older Sierra adventures, I guess the best strategy is: Save often, and in as many different slots as possible. (Because every screen probably features at least one way to kill you, and should you run into a dead end and know what caused it, if you've saved the game at many different stages, you might be able to continue your playthrough by reloading an earlier savegame and this time avoiding what got you trapped.)

And a psychological advice, based on personal experience: If you're anything like me, best try to avoid walkthroughs as long as possible, because once you've looked up one thing, you'll soon come back to look up another once the next problem presents itself. You will get lazier and more and more impatient, and the more often you use a walkthrough, the less happy you will be with the game and yourself. Sometimes I make a note whenever I had to check a walkthrough and write down the reason why I hadn't managed to solve the puzzle on my own. It's interesting to compare afterwards, how much of it was due to my own impatience or serious oversights, and how of much of it was due to really bad game design (often it's a combination of the two, like the game teaching you certain rules that you come to take for granted, only to suddenly break them without notice).

I ditto tinyE click on everything. Learn everything you can. Look at everything you can. try to pick up touch /use everything. Even if it is not logical.

I have not played King's Quest (not a Sierra fan), but I think those apply to most, if not all, P&C games

-start every part of the game just by going wherever you can, picking up whatever you can. Don't start "solving" things untill you're reasonably sure you've got everything you might possibly use, or you'll just waste time

-exhaust all dialogue options with everyone - some may seem really pointless, and often will be, but every once in a while that seemingly pointless bialouge option will actually trigger something necessary

-try to "get into" the game - some P&C games are indeed pretty absurd. But there is often a certain twisted method to their madness. After playing for a while you'll likely to start understanding the peculiar logic of the game world, and what would not have even occured to you before will seem perfectly natural.

-don't get obsessed with what you think the solution to a puzzle should be if it doesn't work - sometimes you'll come up with a solution that makes sense, but isn't the one the designers had in mind. You may end up trying various ways of triggering that solution you've convinced yourself is the correct one, when in fact it's something else entirely.

-Concentrate on what you CAN do - if you're stuck with one problem, forget it for the time being and move on to another, and so on. Often getting halfway with one puzzle will unlock something that will help you to proceed with another and vice versa.

-don't use walkthrough untill you are utterly stuck, preferably take a break from the game, then try again before looking the answer up. Don't ever use a walkthrough on impulse. You;ll end up skipping most of the game.

-If you truly are stuck, and end up using a walkthrough, don't feel bad about it. It's all about having fun, and when solving a puzzle stops being fun, then skipping on to the next part is the sane thing to do.

It depends on the style of adventure really, but with most point and click adventures I play through the game as an explorer. Like has been said, just look around at everything which seems interesting - eventually you'll stumble upon the solution to puzzles either via them being logically sound, the game dropping hints in descriptions, or just from playing enough games in the genre that you can preempt what the designer was going for when designing the puzzle.

Occasionally you'll stumble upon a point which stumps you (again, depending on the style/studio behind the game) and it's tempting to go straight to a walkthrough. At this point it's likely to be one of a few specific things causing the problem: either (1) you missed something you can interact with, (2) you interacted with something previously but didn't exhaust your options, -or- (3) there's some illogical solution to the puzzle which you'd be unlikely to find unless you used everything on everything in every way possible.

In the case of the first point, pixel-hunting puzzles are less prevalent in modern games but they do still pop up from time to time. It's worth in these moments to backtrack through some areas to see if there's anything you missed, or anything new which has opened up. In the case of the second, especially make sure to check your inventory. Probably half the times I get stumped by a puzzle are because I didn't realize I could interact with or modify something I've already picked up.

On the final point: after I've looked around extensively and checked my inventory, for most games I would usually look up some form of hint or glance at a walkthrough. Some purists look down on this, and when I was younger I probably felt the same way - but after so many long years of playing adventure games coupled with a lack of time to play, I'd advocate looking for hints over being frustrated and being put off the genre altogether. I would say to try to hold off as long as possible though, as it does tend to cheapen the game.

I also agree with what has already been said about Sierra not making the easiest adventure games to get into. Not sure which games you played as a kid, but if you like the idea of the point and click adventure I'd really recommend branching out and trying some others in the genre. The early Lucasarts ones are charming and the remakes are decently made. Wadjet Eye also produces some games with really great stories. I'll stop there as this is already a wall of text and you weren't looking for recommendations, but if you're interested I'm sure there'll be lots of people around here who can find you a game for your tastes.

This. Dear god i'm bad at this genre, but I do like playing it. Especially Maniac Mansion.

As tinyE, Leroux, Sage, and Breja have all said, sometimes you'll need to resort to clicking on everything (combine the "rubber chicken with a pulley in the middle" with the "red herring").

However, a good adventure game (in my mind anyway) is one that won't be that obscure in terms of helping you move forward and pushing you along the main path. If a game is well designed/written, you should be able to use simple logic based on what you've learned from other characters or discovered in the game's environments to overcome obstacles and solve mysteries.

For example, the code for a locked safe in a homeowner's study might be the birthday of the owner's daughter, which (in a reasonable adventure game) might be marked on a calendar in the kitchen (right out in the open, but easy enough to overlook). In an unreasonable (or poorly designed) adventure game, the code might instead be a sequence of chirps from a bird outside a window that you have to count and translate into a series of numbers for the safe combination.

Upon solving a dilemma in an adventure game, you should probably be thinking, "Ohhh... that's so obvious... why didn't I work that out faster?" - Rather than, "What the frak? That makes absolutely no sense and I never would have figured that out." :/

Unfortunately, like Leroux said, adventure games do occasionally lack in the puzzle design department. I enjoy playing them for the intricate storytelling and detailed character interactions - and despite encountering these design flaws and me being pretty much the worst at puzzle solving, the adventure game genre remains my favorite. There must be something entertaining about it (at least I hope, or I've just been torturing myself all my life).

There are a couple adventure games that come to mind that are more intuitive than logical, so I can't fairly suggest a general strategy for every one of them, though what gets me through to the end of these games (without walkthroughs) is an appreciation of the journey, of the time spent immersed in the experience. Rushing through adventure games, especially when they are often very short, has never felt fulfilling to me.

Frustration and the pounding of the head against the wall repeatedly are side effects of any attempt to take on a game in this genre without a walkthrough, but - ultimately - solving the challenges you face (on your own) should bring you a sense of achievement, and hopefully some joy as well.

I really like what Goatbrush just wrote in response. Had I read that before writing all of this, I probably would have simply commented, "What the Goat said." :)

Good luck on your adventures, GothikOrk.

If you play an adventure game made by Sierra, save early and often.

Is it even possible to get "good" at this genre? I've been playing adventures for 2 decades, and I do feel like I'm getting faster & better at beating them with no peeks at a walkthrough... But I'm still not sure whether that's because I somehow improve at predicting the unpredictable solutions, or it's just the modern adventures getting simpler and simpler.

Depends on the game. Each company/developer has their own specific style and formula which you'll need to apply. You've gotten a lot of good tips already, so I'll talk about King's Quest in particular:
SAVE. SAVE OFTEN.
Sierra games are notorious for having you die if you so much as fart in the wrong place, and there's nothing worse than making half an hours' worth of progress only to lose it all because you misclicked and stepped off a cliff. If you do something of even mild significance, do yourself a favor and save. Get in the habit of doing it frequently. More modern PnC games immediately transport you back to the point before you died, but the older ones typically made you rely on your own savegame.
Also, there are multiple ways to solve things. If you care about points, you'll get the most by solving it in the most clever way. Never use brute force if you can help it. Always try the non-violent way first, and only switch to beating the crap out of something if you can't think of any other method.

Probably the latter.
The only way to get "good" at the genre is if you can successfully get in the mind of the game designer. You have to think of what they would have you do and what kind of puzzles they'd throw in. Do you go moon logic, constrictive solving, out-of-the-box, or guesswork? Do I waste time trying to find the combination on this safe, will it be listed on the safe itself but somewhat hidden, or does it turn out that the safe is fake and I need to swing it open from the middle like a door?

One thing noone seems to have mentioned explicitly yet is, if you're stuck, try combining items in your inventory. Start by checking if you have any items that might logically be combined into something else (a rope and a hook, for instance), but beyond that, sometimes you simply have to try to apply every inventory item to every other inventory item.

This can be a more or less frustrating experience, depending on the game. In some games, the interface locks up every time your character has to say something like "I don't think I can use these two together", so you have to wait for him to finish before you can try again. Worst of all are the Telltale games though (or the old ones at least, I haven't played any of the newer ones, so I don't know if they've changed it), since in those you can't simply choose one item and click on another. No, you have to drag one item to a special slot in the GUI, drag the other item to another slot, and then click a "Combine" button. It takes absolutely ages.

A general strategy? Heaven's no. Actually yes : drink lots of coffee!

If you don't mind the graphics (I luckily don't because I get a massive nostalgia kick from them), there are some pretty fun adventures that came before the point and click genre : the old sierra games in which you type in keyboard commands for what you want your character to do, e.g. 'look in drawer', 'open door', ''talk to man' etc.
Those type of adventure games are the only ones for which I have anything approaching a general strategy : on every single screen type 'look' or 'look around'. The game will give you a brief summary of your surroundings. Then, for every single thing X mentioned in the summary, walk to it and type 'look at X'. The way the game describes things by doing this will give you loads of hints of what to do/try.
For later point and clicks the same still works, sort of, but now you no longer get a summary by simply typing 'look'. Now you have to use the 'look' icon and click on every damn thing that looks even halfway interesting :P

Put normal logic to the side, but don't throw it out entirely.

Yes. Use your mouse to point at somethin, then click.