Read the float guidelines if you are decorating the pontoon boat for participation in a boat parade. If you are decorating your boat for another occasion, you'll have free creative reign.
Decorate based on a theme you have decided on. Keep the occasion in mind for which you are decorating the boat. It may be anything from Independence Day, to Christmas to the honoring of a specific topic such as a sports team or type of animal.
Get out your basic ideas on paper. You don't have to be a skilled artist to do this. If you can draw, make separate outlines of the inside and outside of the pontoon boat and sketch in the decorating ideas you have. For those not comfortable with drawing, write out a list of your ideas. Having some type of written ideas serves as basic guidance and planning.
Obtain all the necessary tools and supplies needed for your plans. This may involve a trip or two to a hardware or craft store. Items that are commonly used in boat decorating include Christmas lights, flags, banners, garlands, wooden props and aluminum foil.
Clean your pontoon boat on the inside and out as thoroughly as possible. Vacuum the floor, wipe down the seats and tables and rid the walls of any grime. Having a clean area to work with prevents dirt from sticking to any of your decorations and makes a better impression on parade judges or anyone else who will see your boat.