Here are some basic instructions on installing a kit yourself:

Before Starting: It is important that you understand, before starting, that you know how to properly clean and prep the surface where you will be installing the new parts. Here is a quick guide:

Use a cloth and either grease remover or lacquer thinner to clean and thoroughly remove dirt and grime from the surface area of the car where you be applying the double sided tape. Once your finished cleaning, use an adequate amount of adhesion promoter to apply a thin coat to the surface where you will be applying the tape. Make sure the adhesion promoter has enough time to dry before attempting to install any parts.

If you're interested in saving some money you can install a body kit yourself instead of hiring a professional.