You can't start looking for a house until you know how much house you can afford. Typically, a few elements determine that.

First, there is your budget. Beyond the monthly mortgage, you'll have to account for property taxes and possible mortgage insurance, and for related costs like home maintenance and homeowners insurance.
Next, make sure you have enough savings to cover closing costs and a down payment. Lenders typically prefer a 20 percent down payment, though some will accept less (but it might result in a monthly fee, called private mortgage insurance, tacked onto the loan).
Finally, you'll want to know how much you can borrow. A mortgage lender will review your financials (your income, employment history and debt load) to determine that. Experts say getting preapproved for a loan before you start your search will help you act quickly when you find the right home.