Grammar workbooks and worksheets are one way to practice and prepare for the test. While I think these will help some students, I also don't think they're the best strategy for everyone. Be sure you understand the concept before you spend hours working on worksheets and drill. They also have a second language computer tutorial that might be helpful as a review of basic grammar instruction. If you speak a language other than English at home, you may find the ELTI resources particularly helpful.
Some publishing companies have grammar software that they sell.
I've seen students change correct answers to incorrect ones. When in doubt, go with your first reaction to a question. You've been speaking and writing this language for a long time. Schedule your study time so that you're not working on grammar concepts for hours and hours at a time. Allow yourself time to re-take this test, if needed.