Does your opponent float or does he give the impression he is a calling station? It is not an easy task to determine what kind of player you are facing, but it is an important skill to aquire in order to make correct decisions. Questions like "Can I play a second barrel here?", or "Can I check/raise my opponen?t" strongly depend on your impression of the opponent.
In certain spots, you should a guess how high the risk of facing a potential float is and how you could use it to your advantage.