If one player is weak on a colour complex (has no bishop of that colour), and the opponent has that colour bishop, and the queens are on the board, that weakness is likely worth more than one pawn. Dan Heisman, ChessCafe.com
The English Opening is basically geared to controlling the d5 square. White starts off with 1.c4, follows up with Nc3 and completes the job with a kingside fianchetto. Gary Lane, Ideas Behind Modern Chess Openings: Black
Stockfish is a wonderful tool, but remember: it's not enough just to notice that the machine recommends a move - you need to understand why. If it's not immediately obvious, play a natural move for the other side and keep digging until you'd be able to explain and demonstrate to another player why the machine evaluates things the way it does. Andrew Greet, Chess magazine
Few sacrifices work if the attacker cannot bring several pieces, particularly the queen, into the attack with great speed. David LeMoir, Essential Chess Sacrifices
There will always be times when your preparation or memory fails you (in the opening) and you have to make it up. In these cases you should aim to find a move which is sensible on general principles and which does not have an obvious refutation. John Nunn, Grandmaster Chess Move By Move
Don't just study variations in your repertoire; investigate the typical endgames that can occur from different variations as well. Andreas Tzermiadianos, How To Beat The French Defence