powerwashing

i know its a little self explained but powerwashing is needed for your decks, prior to you staining or sealing them this ensures, that you have the proper adhietion to the surface ,please note that the stronger the psi on your machine the more damage you may make if you are doing this as a homeowner, i always recomend that you hire a pro to do this, where they have many different tips for the typeof surface.
there are many stains for the job as well, you may want to talk to your home improvement store, and your contractor what will be best for your project, the better the stain the longer lasting it will be.