Like most people, you will probably wait until submitting a purchase contract on a home before applying for a mortgage. By then, not only will you know the specific property you want, but also how much you need to borrow. At that point, the lender will require that you fill out a loan application and reveal specific information about your current and past financial situations.
The following checklist is a good place to start for gathering the information you will need:
Original purchase contract (the loan officer will make a copy and return the original to you)
Copy of earnest money (deposit) cancelled check
Employment history details
Last two years