Spend time and money on the landscaping and the outside of the house. This is the first impression that most buyers have of the property and investors often neglect to factor it into the financing of the project.
Flippers need to remember that the house is an investment. Don't become so attached to the house that you lose sight of the timeline for moving the property.
Make sure you plan out what is to be done ahead of time and generally stick to it. Spending more than you planned for can be a disaster for your profit margin when you resell the house.
Don't talk about any deals on houses you have found until you have actually closed on the property. If you brag too much about the steal you've found, you might find out that someone has bought it out from under you. It's not yours until your name is on the papers, so remember that before you say or do anything.
Don't get so intensive in your fixing up that you keep the house off of the market for a long time. You need to fix it and put it back on the market in order to invest in another property.
Know the value of the house and the statistics for the neighborhood that it is in. Pricing a house too high in a neighborhood is a common mistake, and having knowledge of the area will prevent that.
Make sure you have the house properly inspected. A deal of a house usually has something wrong with it, and an inspection will tell you if it's a problem that's worth fixing. A lot of buyers focus on the deal, and not what it will cost them to fix the deal so it can be resold.