Overcards:I miss the flop and someone bets big;I usually fold unless the pot is big and if I know the odds of my out being counterfeited are low.For the most part you are drawing to 6 outs presuming your outs don't give someone two pair(or worse a straight).For the most part I dump my overs when I miss.

Straight/flush draws:I call if the flop bet is decent and if I know doing so will encourage other callers(pot odds).If I am last to act and everyone has called I may raise to represent a made hand(and again induce calls to either up my odds or better yet folds).

Turn I lead out if I raised the flop betting.I check if the free card is avaliable.Sometimes I'll push all in if I have a pair and I know the others are capable of folding.

River is straightforward:valuebet if you hit,check/fold if you missed.The times you hit should at worst balance out the times you miss.