[W. Deranged]

The key to check-raising is relative position.

If you are trying to generate value :

-Check-raise if a bet is likely to come on your left, as you will most likely face multiple opponents with single bets.
-Bet if a bet is likely to come on your right, as check-raising forces opponents to have to call two cold and will generally hurt your action.

Conversely, if you are trying to protect your hand :

-"Flip 'em": Check-raise bets on your right and lead into bettors on your left, looking to face the field with two cold and encourage folds.