Here's what you'll need to get the Pre-Approval process started:
One month of most recent paystubs
Two years most recent W-2's (1099's if applicable)
Two years most recent federal tax returns (if self employed)
Two months most recent bank statements (all pages with bank name, your full name, and full account number)
Copy of most current 401k, mutual funds, etc. (all pages)
Copy of Driver's License