Calculation shortcuts

Can you please list your calculation shortcuts?  You know, the little shortcuts that save your clock and don't require a lot of calculation.  Here's two examples to get us started:

(1) placing two pieces or a piece and your king on opposite colors so that a knight can't create a fork.  Very useful, especially in an endgame when time can be tight.

(2) placing a bishop 2 squares away from a knight so that if the knight makes a move in the direction of the bishop, it can be captured by the bishop. 

Rule of the Square for king and pawn endgames.

http://en.wikipedia.org/wiki/King_and_pawn_versus_king_endgame#Rule_of_the_square

Learn basic positional rules and ideas, and for the endgame study basic endgames for all piece combos and different pawn distributions (such as three pawns on one wing, two vs. one pawn on a wing, three vs. two, kingside vs. queenside majority, etc.)

How about, if you place your knight on a diagonal from a target square, it will take 3 move to hit that target (in other words, you should choose a faster route).

More useful for king and knights IMO is placing it two squares away diagonally (minimum 3 moves to give a check) or three squares away orthogonally.  And in both cases the king covers the two squares closest between king and knight which also helps protect an area e.g. if you're trying to queen a pawn.

now that's a useful tip.....appreciate it.  what do you mean by "orthogonally"?

It means up, down, left, or right, what "diagonally" is not.

Perfect!  I think I learned that one many years ago and completely forgot about it.   Very useful my friend!