Like it or not, most exterior house painting projects will be about 80% preparation. In those cases where the preparation can be almost entirely skipped, there's usually no need to paint the house. It can just be cleaned.
Also, despite the existence of power tools that can be helpful, most of the job comes down to good old elbow grease. There's no getting around that it requires a fair amount of tedious scraping, sanding and cleaning.
But the results will make the effort seem worthwhile in the end. A well-prepared house exterior will make paint go on quick and easy and produce a smooth, superior shine.
The amount and degree of effort depends, of course, on the condition of the house and the surface to be prepared.
Peeling paint will take longer to deal with. Scraping and sanding is a must. Any areas of mildew will need to be treated for removal, then treated again to protect the wood before painting. Aluminum siding, on the other hand, typically requires no more than a good wash followed by possibly a spot sanding.
Inspect the surface. Look for areas of peeling paint. A 6-8 inch scraper can usually take large areas off with a little bit of effort. Rarely is it necessary to remove every scrap of paint, just any sections that will continue to peel. For areas close to angles and smaller sections a smaller scraper will be needed.
Next comes sanding. It's pointless to simply sand off layers of dirt. So, before beginning, give the surface a good wash. Power washers are available, but most are so powerful they can easily gouge wood. In many cases a bit of TSP (trisodium phosphate) and a garden hose can do the job. For areas beyond easy reach, a car washing tool with an extended arm can be a great aid.
Allow the surface to dry thoroughly before sanding. Sanding wet wood will rip the fibers, making for a very rough surface. Sanding wet aluminum siding will considerably shorten the useful lifespan of a rectangle of sandpaper. Drying may take a day or even two depending on the humidity, temperature and time of year which affects the number of hours of sunshine per day. To be completely sure, a moisture meter can measure the moisture content in the wood.
Sand any area thoroughly that needs it. Which are those? Areas where peeling paint was removed will usually have edges. Sand them down smooth. Areas where the surface contained mildew need it. Any section where a rough spot resides or putty was applied to a gouge. Anything that looks rough or sharp at that stage will appear magnified once the paint is applied.
For the final step, another good wash is essential. You don't want to paint over the dust left by sanding. You need a clean, dry surface that will allow paint to be absorbed. Dust will hinder absorption and new paint will begin to shed or flake off soon after.
Now for the easy part. Painting.