here is a
great digested post by jrz about firing the second barrel. sure, it is about betting the turn but it is a great read and is a continuation of stuff to think about AFTER you fire that bet on the flop.
For me, there are no hard and fast rules and it all depends on so many things othat have already mentioned. Also dont forget that YOUR perceived image is important.....ive had sessions where I c-bet too much (eg if im tilty or being smacked it the face by the deck but they keep folding so dont know I was pure value betting) and of course, every stops believing me so I lose the ability to take the pot on a bluff
OZi