From the Guidelines page of Dan Heisman's site:
"Don't be afraid of losing. Be afraid of playing a game and not learning something."
"Don't play a game or even a move if you don't feel like trying your best."
"It always struck me as strange that someone would study something subtle that could take one from 2300 to 2303, when what they really needed was something basic to take them from 1400 to 1450!"
"Think of a draw offer as an offer to remain ignorant of what you would have learned in the remainder of the game."
"Never start a game without the intention of using almost all your time! If you don't feel like playing that slow, instead play a game with a shorter (faster) time limit."
From the Quotes page of Exeter Chess Club:
"All openings are sound below master level." (Lombardy?)
"A combination composed of a sacrifice has more immediate effect upon the person playing over the game in which it occurs than another combination, because the apparent senselessness of the sacrifice is convincing proof of the design of the player offering it." (Richard Reti)
Chess Mail (a great place to play live chess or tournament play)