practice tests as possible under normal test conditions. Follow the timing rules and everything. When the tests are done, grade them and keep track of what the areas of weakness are, not just the section, but get specific. Whether it be fractions, verb-noun agreement or whatever. Then attack those areas one by one.

Public libraries often have prep books available to loan out. Find all of them within a 10 mile radius, and take all those practice tests. Thats the best bang for your buck system. Don't pay for the books when you can use them for free.