Think of all possible actions and sizings you make, then do the same for your oppoent, then decide what the most profitable course of action is.
Most of the time the only thing I am doing is thinking in what way my opponent could be doing wrong and try to exploit it, if I can't find a leak I'll just play a safe and balanced game. SPR and such are useful because they give an indication of what kind of money you can put into the pot but eventually you'll want to look into more detail.