You learn to take decisions with vague information by approximating and using basic math. As TomGullen says, the necessary math is neither hard nor is it much. To art is to adapt your numbers to the real world situation. Example: With an open-ended straight draw at the flop, you chances are roughly 1/3 for a straight in the end. First, you need at least two other players. If you have one other player, you fold, because it is not profitable. With three or more other players you keep playing. With two enemies it gets interesting, because you need to factor more information in, to decide. What is your position? Did someone raise before the flop? How did your two enemies play their hands before? What is your image at the table? ...
Another lesson i got from poker is to control my emotions when I'm on a streak. If you are on a winning streak, you still must fold when the math says the expected value is negative. On a loosing streak you still must go all-in if the math says so. No peaking at the flop, when your initial hand is too bad.