1. Don't practice beyond your abilitySo let's face it, most of us here who practice regularly often practice a bit too long at times. To a point where the playing gets redundant and monotonous, and the fun of practicing just seems like it fades. When this happens, a break is probably what you need, just to keep things fresh. This does not apply if you're a lazy-ass and don't practice as much as you should to begin with, but only for those who practice the same things a bit too much. You might even injure your fingers by pushing yourself too far too regularly, and no guitarist wants that. A break is mandatory to calm your own mind, and let the creative juices flow and refresh themselves, and if you have done that, I'd like to go to my second point.
2. Don't practice things that you are already good atWe all know this one. When you can play something kind of well, you feel like playing it again and again. In general, and from my personal experience, it's a lot of fun! No question there. But the problem with that is, assuming that you are an average player, you must have some weaknesses. If you're good with legatos, maybe you have problems with bending. If you are good with vibratos, maybe you aren't perfect with sweeping. And I don't know about the next player, but I would generally like to learn all that I possibly can. So, frankly speaking, if you're bad at something, practice that over and over again, instead of what you already got nailed down. You'll improve, you'll stay motivated and your overall playing skills will get boosted. The distance between you and being good at a technique you're bad at, is the will to master it. Simple as that.
3. Try to stay open minded about musicSo this is a weird, but important one. Say that you're a blues player, but you happen to generally dislike a certain other genre. The problem with this is that, you never know what this other genre might be doing with their playing style. Who's to say that they don't have blues influence? No one. So when it comes to listening to, or trying to different styles of music, it's best to give them a try no matter how much the majority doesn't like or approve of the artist. You never know where you might find inspiration.
4. Start experimenting with what you already knowI don't care if it's a song, or a scale, or just one riff. Play around with the notes of what you know. Play in a different tuning than what you normally play at! If you know a small melody, play that at a different octave, or play that with a harmony over it, play it in a different position than where it's supposed to be. If you know a scale, try playing it in triplets, if you've played it in triplets, play the scale over different chords. See which one works and which ones sound bad. Try figuring out stuff with ear. This is a major way to get out of that rut and that lack of improvement. Experimenting and playing around with random stuff often leads to more than just that. You end up learning new stuff, and get newer ideas. And most importantly, it's fun to play around like that, well, that is if you're willing to learn.
5. Stop trying to be a carbon copy of someone elseThis goes without saying, we're all different, and our playing can never be the exact same because of how different our arms and hands are. Someone has a longer thumb, someone else has a short thumb. Someone has long, stiff fingers, someone else has smaller, more flexible fingers. It isn't necessary to point out that what works for one person, might not work for another. We're all different, as I already said. If you're trying to play a guitar solo played by someone with significantly different hands, you probably can't master that same solo in the style that person played it in. You need to find what suits you, how you are comfortable and how your fingers can move more freely on the guitar. Remember, the greatest guitarists are born from originality, not from being carbon copies. Never try to force yourself to play like someone else, for the best that you can be as a guitarist, is by being yourself. You'll know what I mean if you've been playing and learning the guitar for a while now.
That's about it! I hope this helps people who are striving to improve, or are stuck in a musical rut. May the force be with you.