Need Help - 4 weeks to go

Dear All,

I am a frequent visitor to this website and need some advice on my current situation. This will be my third attempt at cracking the GMAT.
My previous scores were:

- 480 (wrote it in Jan 2008)
- 600 (wrote it in Aug 2008)

I will be writing it again on 5th Jan. I am much better prepared compared to the last couple of times but wanted to know how long should i wait before i start writing the practice exams. I have taken two weeks off before the exam.

Thanks and Regards,

Raj