Whether you c-bet depends on many factors. How many opponents called your raise preflop? How do you rate your opponents? Bluffing calling stations is money wasted. And then it also depends on how your hand is and which cards came on the flop. Let's say you raised with AK preflop. The flop comes Q83 rainbow. Apart from a weak draw, namely 2 overcards, you have nothing. Still, I'd raise one or two opponents on this flop. They may also not have hit anything and will get out. You can also represent a top pair because you may well have raised with AQ preflop. It looks different if the flop brings T9J and two cards have the same symbol. The flop is very drawy. Many opponents can have hit something. Here I would advise against a c-bet if you haven't hit anything yourself.
The bet size is usually between half and 2/3 the pot size. If you decide to C-bet, the size of the bet depends on two factors. How many opponents do you have? How draw-heavy is the flop? If you have 2 opponents and the flop is draw-heavy you have to increase your bet size.
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