Brush out the edges around doors, windows, floor, electrical outlets, and ceiling. Then use a roller to fill in the large areas. Mulitple, thin coats look better then one thick coat and prevents drips and runs.
Move your furniture to the middle of the room then cover your furniture and floor using plastic! Then tape it down and tape your trim! Then you are ready!!
Focus on one surface at the time. Get everything out of the way. Clean the surface you want to paint with a brush or vacuum cleaner. Tape off other surfaces. Cover floor with old newspapers. Cover furniture with plastic sheets. Use a brush in corners, a roller for bigger surfaces.