Figure out how much you can spend before you look at any homes. Most lenders will qualify you over the phone, and many have online financial calculators to tell you how much money they should be willing to loan you. The important thing to remember is that you need to be comfortable with your payments, including taxes and insurance. Your qualifications may allow you to borrow $300,000, but if you are not comfortable with the payments that accompany that amount, you may want to purchase a home in a lower price range. You want to have a life outside of your house, and you certainly don't want to find yourself strapped to a mortgage that doesn't allow you to live the way you want to live. Draw up a budget and figure how much you can spend on your mortgage without compromising other things that are important to you, and stay in that price range. Then have your lender issue you a pre-qualification letter that can be presented with any offers you may make on prospective homes. This solidifies the fact that you can afford this home in the eyes of the Seller, and will make your offer more attractive.
Do not look at homes outside of your price range. Viewing houses that you realistically aren't going to be able to buy will tend to cause problems. After seeing what they have to offer, it can sometimes be difficult to drop down in price to a home with less square footage or fewer features. Compare apples to apples and if you truly can't afford a property, skip looking at it. Exceptions to this rule would be: if you have the ability to purchase more but preferred not to, but now you are discovering you can't find anything acceptable in the range you are currently viewing; if your agent has knowledge that the owner of a home is needing to sell and may be willing to drop their price far enough to make it affordable for you.
Be honest with your agent AND yourself. If you truly hate split-foyer homes and would never, EVER live in one, then don't look at them. If the right one could be an option but you would prefer a two-story or ranch, look at the other floor plans first but then view a few split foyers as well. Keeping your options open may help you find a home you love that you might have otherwise missed.
If you are in your first round of home viewing and go through a house that fits your every need and you absolutely love it - GO FOR IT! There is no guarantee it will not sell to someone else today, even if it has been on the market for awhile. The worst part of losing THE home to another buyer is that you will now compare that home to every other one you see, and it will be very difficult to find one that measures up. Trust your instincts, and be happy you didn't have to trudge through 100 houses before you found the one that is right for you.
After you find the right home and get your offer accepted, you still have many things to do. There are inspections, an appraisal, contingencies to release, and closing documents to prepare. Your agent and lender will help you keep on top of all of these, so please get them any information they need as quickly as possible. Time is of the essence in all Real Estate transactions. After all contingencies are released and it appears the purchase will be completed, call to have utilities on the new property switched into your name as of the date of possession. Also call as soon as possible to secure movers, if necessary. Then attend the closing, sign the many, many documents, pick up the keys and enjoy your new home!