if you think they're on a draw calling your flop bet, you can try to price them out of it on the turn.
hmmm. if youre that sure that they are on a big draw (8-9) outs, i think its best (with air, or air-) to check the turn and bet the river if it appears theyve missed. with a lot of players, youll have to make a bigger turn committment than its proabably worth to knock them off the hand. if you get called on the turn, the pot has swelled so much that the hand is played out completely differently on the river.