I think that all the best things you can do to get the best rate possible happens before you even shop for a mortgage. By saving as much as possible towards down payment and making sure your credit balances are low and all your bills paid on time, will put you in a position to obtain the best mortgage rate and terms.
i also tell people to NOT shop interest rates alone, but rather shop for the Loan Officer and/or mortgage company you feel will provide the best service along with fair rates. i've seen many people who go for a particular company simply because they offered the best rate, which almost all the time is not much different than what other banks offered, but yet have problems closing loans. You have larger banks who offer lower fees and rates, but is not willing to approve your loan because they're extrmemly conservative, then on the other side you have companies who are willing to take all the risks in the world to approve your loan but fees are through the roof. Find something in the middle, a bank whose menatlity is "every loan matters", a bank or Loan Officer who is known for working with Realtors and homebuyers, and delivers. This assures that the people you're working with see a variety of situations and have the experience necessary to deliver good service to a homebuyer. There is no way you'll get that over the internet or a phone.
Senior Loan Officer
Sterling National Bank