I have lurked these forums for a bit but I am new here, forgive me if this post doesn't follow normal posting etiquette.
I noticed that this forum "Student's Corner" has a lot of people asking questions, but few threads with general advice and answers. I am not expert at piano but I think I can give some advice that I haven't read else where (or perhaps advice that I have read else where that I feel should be emphasized.
Disclaimer: I have only been playing piano for 2 years, I have taken classes at my school for these 2 years. I am by no means an expert.
Tips and Advice:
If given the option to choose a piece, choose one you WANT to learn. This will make some long practice sessions a lot more fun.
Don't zone in on one part of a piece for hours and hour at a time, after a certain point it just becomes inefficient. Instead take breaks, work on other parts of the piece, or on other pieces.
Pay attention to the sound that you are making, you should know how your piece is supposed to sound, try to play your piece beautifully in your head while you are playing it.
Keep your back straight, when playing difficult chords [for me at least], a straight back is crucial to get your fingers in optimal position, stops your hands from falling asleep, and allows blood to travel better so you get less sore. [i was playing with my back bent for hours and noticed after making the switch to a straight back only after an hour or so that my hands felt significantly less tired]
Don't be discouraged if you have to play 1 measure over and over, with only one hand and you still can't get it right. The more you practice now the less sloppy it will be than if you rush it. And an accurate but slow performance is better than a quick but sloppy one.
Don't keep making the same mistake over and over and expect it to work itself out later. This tends to develop bad habits and makes things harder to fix when you're used to playing something wrong. Fix your mistakes right away and practice SLOWLY.
Playing a piece well has multiple aspects to it. Proper speed, perfect note accuracy, and proper dynamics. Don't forget to listen to yourself as you play, have an idea of the sound you want to make. If you can play a piece well you shouldn't be worried about where your hands go next AT ALL. When I play a piece, that I've practiced and memorized, I try to meditate and match my emotions to the notes. It sounds cheesy, but I think this is the difference between playing all the notes of a piece in time and playing and actual song.
These are just the first few tips that came to my head. They aren't that original but hopefully this puts a few pieces of good advice in a single area and is a bit more specific than in other areas you may have read the same or similar advice. Please post any other advice, and criticism! Especially criticism, I don't want to tell people to do the wrong thing!