What I always tell everyone is to know your own finances!! Mortgage companies ALWAYS approve you for a larger loan that what you can probably afford! Whatever amount they approve you for, subtract about 40K off of that & it will give you what you can realistically handle.
If you have your property taxes paid in escrow, make sure they are adding the right amount to your mortgage payment to cover the taxes. When we bought our house several years ago, the first year, our payment was just under $900 a month. At the end of that year, I got a call from the mortgage company: They had figured our property tax based on an unimproved lot so we had not paid enough in that year. Their fix: The second year in our house, our monthly payment was approx. $1400! The third year, the payment went down to about $1200....what it should have been from the beginning. I thought this situation was just a fluke, but it also happened to a friend of mind just a couple of years ago & since then I've found out it seems to be fairly common.
If you are buying in an established neighborhood, don't be shy about knocking on someone's door and asking them how they like their house. If they've lived there a year or two, then they should be able to tell you what problems they've had with the builder...do they have leaks, does water come in under their back door when it rains, plumbing issues....etc. You'd be surprised all the problems with new construction houses!!
And finally, don't get an ARM loan (adjustable rate). Go for a fixed 20 yr note....the payment isn't that much more than a 30 yr fixed & you'll pay 1/2 the interest. For example, (for simplicity's sake) say you are buying a $100,000 home....for every 10 yrs you are paying on it, you will be paying the sale price in interest. On a 20 yr note, you will end up paying a total of $200,000 for your home over the 20 yr period. If you get a 30 yr loan, you will end up paying $300,000 for your home over the 30 yr period.
Good luck with your search....read, read, & read again EVERYTHING you can find on the internet about buying a house.