Not budgeting for all your housing expenses. Your monthly payment for a house involves more than the principle and interest. You'll also be paying for property taxes, insurance, utilities, and homeowners association (in some cases). You may need to set aside money for repairs and regular maintenance, such as exterior painting, fixing up the yard, and cleaning the yard. If you intend on remodeling, such as adding new kitchen cabinets, that has to be factored into your expenses as well.
Assuming your first offer will be accepted. Almost nobody accepts a first offer unless the seller is truly desperate or he priced his home too low for the market. Buyers typically offer lower than what they expect to pay while sellers counter. The process continues until a final price is negotiated. An exception to this is when a house has multiple offers. In that case, your first offer generally has to be your best one.
For more information on how to buy a home, please contact us.