Preparing the House
The first thing you want to do when installing your siding is take a close look for any problems that might exist with the structure of the existing siding or sheathing.
If you have an older home with wood siding that is past the point or too much trouble to paint every couple years you want to make sure that it is structurally sound. It doesn’t have to look pretty since you will be covering it up but it does have to be free of rot and bug damage.
If you find a section that needs replacing you can use half inch exterior grade OSB or Plywood to fill the area. You want to make sure that your repair is flush with the existing material you don’t want to just nail on plywood over top of the bad area.
Vinyl Siding is very forgiving to slightly out of true and flush surfaces but you can’t hide the world under it.
You will also want to take this time to bleach and pressure wash any mold off of the siding and then go around and caulk any areas around windows or other large gaps where bugs may get into the house. Again you are not preparing the home for paint you are just fixing structural type problems.