check any flop that isn't good for a c-bet, and check more often if your PF raise got more than one caller.
Flops good for a c-bet are:
-any you hit a decent pair or better on (obv)
-dry boards, especially with one high card such as A or K
-wet flops that you hit a draw on
-virtually all flops when you are heads up ESPECIALLY if in position and it's checked to you
You can also look at the FoldtoCbet% stat if you use an HUD to try and get a likelyhood that they will fold to a c-bet
bluff