I think I have heard more bad strategies about guessing than about any other topic related to this test. So let me set the record straight.
If you know for sure that one of the answer choices is wrong -- for example, if the question asks for the absolute value of something, and one of the answer choices is negative -- then you must not leave that question blank, even if you know nothing else.
If a problem seems too easy, look at its number. A number 12 that seems easy probably is easy. But a number 38 that looks easy means: you should take a careful second look to make sure you haven’t missed something important.
If you realize that the best you’re going able to do on a problem is to make an educated guess, then make your guess, mark the question to come back to later if there’s time, and move on. Making the guess is good strategy. Taking forever to do it, is not.
If two answers look equally good to you, then I’m sorry to say it, but you have screwed up. Most likely, you misread the question. So: read it again, paying special attention to any words whose meaning you aren’t sure of.
If you follow these rules, your guesswork will be very good.