There are two major mistakes that can happen when dealing with outdoor lighting.
The first mistake has to do with using poor quality lighting fixtures or bulbs. Outdoor lighting is certainly a thing where making a larger investment first will save you money in the long run.
The second is not consulting a professional. The lack of this can result in over lighting your house along with several other things.
Finally the lack of control in your lighting is the final mistake. Make sure you can turn on and off your lights when you want. Details at: