Remove any vegetative growth from masonry walls, and clean them down thoroughly. Small holes in masonry can be filled using all-purpose powder fillers as long as they specify exterior use. New masonry finishes should not need any further treatment.
Old masonry may need some more extensive repair. It will also benefit from an application of fungicide, and stabilizing solution if the surface is flaky. Once the surface is clean and dry, fill any remaining holes and sand as normal.
When you come to paint walls, the best choice is exterior latex, often called masonry paint. Apply a mist coat — the paint you are using diluted with 10 percent water — followed by two full-strength coats. Paint from the top down, covering the walls before woodwork and metalwork. Some deviation from this basic plan is often necessary because of access. You may find it easiest to paint roof details such as soffits, fascias, and bargeboards, followed by the top section of wall, before tackling the lower surfaces.