By learning how to put opponents on a range of hands. This is probably the most crucial skill required in poker, and you learn it from experience and observation.
Poker is a game of incomplete information. Since we can't see villains' actual hands, we have to assign a range they could have based on their overall tendencies, their position, and the betting action.
Some players rely heavily on mathematical probabilities when deciding whether to raise/call/fold. Others use feel/intuition, but even that is based on (subconscious) math.
Good advice for a beginner would be "When in doubt, FOLD", especially if you're currently finding yourself on a losing streak. Villains don't bluff much at low stakes. If they are betting strongly and (especially) if they raise, they have a strong hand.
Playing in the micros, you should adopt an ABC style. Bet when you think you have the best hand, call when the pot lays good odds to draw to an OESD or flush, and fold when villain appears to have you beat. You wouldn't be making a huge mistake if you folded every time you bet and got raised, as raises (especially on the turn and river) usually mean "I have a better hand than you".
More on hand-reading and ranges:
http://archives1.twoplustwo.com/show...Number=8629256
Complete guide to beating the micros:
http://forumserver.twoplustwo.com/78...micros-430637/