If a paint booth is out of the question, which is a pretty common scenario, the house garage will work fine. Here are some simple pointers to increase painting conditions. Place barriers up to limit overspray. Wet the floor and sweep out the excess water before painting. The dampness will help keep dust and dirt from swirling around. If possible, create a slight draft in the garage by utilizing garage doors, filters, and a fan. This will create a draft and help push overspray out the door, increasing visibility. (Note: this isn't exactly the most "green friendly" way to paint, but it will get the job done.) Before any spraying occurs, wipe the surface clean with lacquer thinner or some sort of paint prep cleaner.