Decipher what you can afford before you begin to seriously shop open houses.
After you are certain that your credit is in good shape, start contacting mortgage lenders to see what you will qualify for. Shop around to ensure you are getting the best deal available.
Do not submit too many mortgage applications. Too many inquiries on a credit report will cause the score to go down. Bankrate.com recommends that all applications be submitted within 14 days of each other, as they will likely make less of an impact that way.