Look around the house for any soft or rotting wood, especially around windows and doors.
You'll need to replace it with new wood prior to painting.
Fill cracks and holes. Paintable caulk can be your best friend on exterior painting projects, but you don't want to overuse it. For instance, caulk is not suitable for repairing large holes; rather, it is best used for sealing the spaces between window frames and siding. Follow all manufacturer directions.