Look at 100+ houses. Drive around, go to all the open houses, pick up all the brochures and flyers that you can find in boxes in front of houses, research, research, research.
Use a buyer's agent, absolutely.
Make your offer contingent upon an inspection and pay extra to make sure termites and pests are taken care of.
Really, really know what you are looking for (after you look at 100 houses, you will probably have a very good idea of what you want and what you can live without).
Drive around all of the neighborhoods that you are considering many times, during the morning, rush house, around midnight.
Right before you tour any homes with your realtor, do a quick check and see where the sex offenders and predators are in that neighborhood. It'd be horrible to buy a house and realize that next door there is a sex offender that did "something" to a child under 12, right? (there is a house like that about a mile from here, cute house, too, but I hope no children move into it)
Make sure that you know what homes are going for in that neighborhood. Ask your realtor (buyer's agent) to print off lists of the homesales in the last month for the areas you are interested in for you to look at. Get a really good idea of what homes in that area should go for, so that if you find a really good deal, you will be knowledgeable enough to jump on it.
Depending on the market and where you live, you might want to consider low-balling. If you offer a low price on 20 homes, chances are that one of them might accept your low offer and as long as you love the house, you'd be getting a great deal, too.
Talk it over with your realtor, first, because some realtors are not willing to lowball, others are willing to give as many offers as you'd like them to give. Find one that you really feel you can work with and one who isn't rushing you to make a deal when you are not ready to do so.
Make sure you know what you can afford and what you want to spend and look in that price range. You might be able to go up into the next higher price range and offer less to still stay in your price range.
We purchased a home at the very tip top of our price range, after considering homes much less that we would have lived in but we would have been dreaming of having other amenities and wondering when we should try to upgrade. Instead, we purchased a home with an extra bedroom and a pool, a fenced yard, decent neighborhood, etc., and we are SSSOOO happy that we did that. We could stay here another ten years (perhaps more) and never want or need to move. Some people suggest buying less than you can afford, which is also great, as long as that makes you happy. We are glad that we stretched our budget a little and feel like we are on vacation all the time.