Cambridge is the best book , try more and more 4 hour practice exam that are available in cds and all.
but these are the book order
1.cambridge-hard & good book
2. barrons
3.kaplan
4.ets
5.longman
6. delta and other books.
you can score yourself and practice accordingly ,in which section you are more weaker try to cover up that first,
key is more practice the higher the score is!