Practice Tips

Now, if you talk to any of the music teachers I've had in the last 10 years, they'll tell you that I shouldn't be making a page like this, or if I was, they'd never believe me. I always manage to find a way to avoid practicing (terrible, I know), but here is the best advice I've heard.

Practice in a well-lit, spacious area. Something bright, with as much natural light as possible.
Unless you're working on ego, play in an acoustically dead space. Yes, it sounds better to play in a huge, echoey chamber, but you can't hear your mistakes as well... which is the point of practicing, right?
Don't practice mistakes. This is my biggest problem in all my practicing. Play it right, no matter how painfuly slowly you have to take it.
Unless you're working on one particular part, play the whole thing through, beginning to end, no stops. Ever had that piece where the 1st mvt. is great, the 2nd is OK, and the 3rd is bad? Ever wonder why?
Never practice for more than half an hour without stopping. (I got this one from a professional) AFter that length of time, your brain just shuts off. It's like trying to study for hours on end... it doesn't work. After 30 minutes, stand up, walk away from the instrument, drink water (especially you singers out there!), have a stretch, go outside, clear your head, and come back to it.
Also, if there's something you JUST CAN'T GET, leave it... for the entire day if possible. Just move on; you're just going to frustrate yourself if you try to work on something that your head won't let you.
Before a performance, try to get at least a couple rehearsals in the performance space beforehand. Try playing in different parts of the hall, learn how the acoustics of the hall work, and play with them.
Unless you own a decrepid old piece of junk, your instrument is NOT to blame for your mistakes... don't take your mistakes out on it! Also, if you're nervous, don't squeeze the instrument, it'll only make your hands sore faster!
BE COMFORTABLE!!!! Play in pyjamas, slippers, bathrobes, or whatever you feel comfortable in. The last thing you should have to worry about is your jeans riding up in the middle of a Mozart Concerto. I prefer PJs and bare feet.