Composites have few maintenance needs, so you'll have plenty of time to take care of the ones that do crop up.
Sweep or blow away any debris between the boards so that water can run off freely. Food stains.
Fast action is the best defense. Use a degreaser such as Dawn dish soap on oily spots, and bleach and hot water on fruit and wine stains. Placing mats around the barbeque is a good preventative measure. Tannin stains.
Scrub with cleaners that contain oxalic acid.
Superficial scuff marks blend in over time, but any board that has deep scratches or melt marks will have to be replaced.Mildew stains.
Add some dish soap to a 50-50 mix of oxygen bleach and hot water. MORE: Editors' Picks: Our Favorite Outdoor Spaces Ever