Step 1: Washing the Exterior
This is the first and most important step as paint simply won't stick well to dirty surfaces. It's safer to use a hose and brush attachment than a power washer as power washers are known to often cause damage to the soffits and can cause warping too. The last thing you want is to paint onto a damp surface which would be prone to mold or mildew growth. Depending on the amount of dirt on the exterior of your home, you may need to use rags and sponges to help remove stuck on dirt. Also consider using liquid soap and or anti fungal cleaner if necessary to remove mold or mildew.
Step 2: Scrapping
Make sure to have your protective goggles on and begin scrapping any loose or peeling paint. For paint that is multi layered or just tough to remove use a heat gun or rotary paint remover which has more power to remove the paint. Use proper safety precautions while using either of these tools such as wearing work gloves and keeping both tools away from your body or flammable objects.
Step 3: Sand and Repair
The next step is to sand the edges of the area where the paint was removed to help the new paint cover and hide the edge. Caulk any cracks, seams or gaps with paintable exterior caulk. It's important to be meticulous near the doors and windows so that the paint will stick properly in these areas. For wood siding, you should also fill any gouges or holes with exterior grade patching compound.
Step 4: Taping and Covering
This step involves taping any areas which you do not want painted such as windows. Also make sure you cover anywhere that you do not want paint dripping onto, including shrubs, bushes, porches, etc. Plastic tarps or drop cloths will do a great job