Before you start house hunting, it's a good idea to know exactly how much you can afford to spend on a house. Otherwise, you'll end up wasting time searching for homes that might be outside your price range. And while you can look at your income & expenses to get a pretty good idea of how much you can spend, you should really apply for a mortgage and find out EXACTLY how much you can afford.
These days getting into debt & damaging your credit is easy. And when buying a house, the more credit card debt you have, the less house you can afford. And the more credit problems you have had in the past, the higher the interest rate you'll have to pay (and therefore your monthly payments will be higher, too). So, if you have any credit card debt, or have had any credit problems in the past, it's a good idea to reduce your debt & improve your credit score as much as possible BEFORE you start house hunting!
Buying a house involves LOTS of little details. That's in addition to all the big details. So when your home search starts getting busy, and you're getting ready to make a decision, it's a good idea to have a professional on your side. But just hiring the first real estate agent you can find (or worse, using the one selling the house) isn't enough. You should make sure you find a qualified real estate agent - one you are very comfortable with - so you don't end up making any costly mistakes!