You might consider a commercial prep course or tutor. It will be worth it--this section is half the test.
In general, becoming familiar with the different kind of questions is important. You might also read up and study about logical inferences and fallacies. Here's the general process I used to get ready:
1. Read the question first so that you know what you will be looking for.
2. Read the paragraph. Pay attention to modifiers such as: all, none, some, most, every, if, only if, unless, etc. These types of words play important roles in the argument.
3. If the paragraph presents an argument, identify the conclusion of the argument.
4. Evaluate the argument. Make sure you identify the relationship between the premises and the conclusion. Spot any flaws.
5. Pre-phrase an answer. Predict an answer based on knowing the question and reading the passage.
6. Go to the answer choices. If none of the answers matches your pre-phrased answer, or is similar, eliminate choices until you have only one or two possibilities remaining.