Before you begin to look for a new home, it is best to pre-qualify for a mortgage so you will know your budget. Pre-qualification is free and it will give you a range for the cost and amount of your mortgage. Pre-qualification is needed by many sellers before they will show you any homes. 

For pre-qualification, the lender will look up your credit score and ask you about your income, debt, and savings to come to an amount their company would be comfortable lending to you.  Just because a lender is willing to loan you an amount, doesn't mean that you should spend that amount on a home.  Look over your budget and determine for yourself what your comfortable spending on your mortgage payment. 

To receive an actual quote for yourself, you will have to provide documentation which consists of providing the lender with information regarding your income, assets, and employment. Documentation ranges from "full-documentation" where the borrower has fully verified sufficient income for the last 2 years, to "no-documentation" where the borrower provides no information on their financial condition. The more documentation the borrower can provide, the lower the risk to the lender, so the better the deal they will receive. If the borrower can't provide full documentation, it is best to met the highest level of documentation they are able to provide, unless they voluntarily choose to avoid it and pay a higher price.

Please note that any advertised loan rates do not account for your own risk profile so don't be fooled into thinking that the company that advertised the lowest rate in their ad will actually give YOU a rate that is lower than their competitors.  To get the best price, you will have to receive a quote for yourself and then compare that quote to other quotes you have received from different lenders.  According to a customer service studies, borrowers who shop multiple lenders tend to be the ones most satisfied with their lending experience.