In general, a decent washing (I use a car specific wash, dish soap is usually harsh and tends to strip wax) and almost any car wax is better than nothing.
Better is once a year or so, a light sanding (say.....1500grit wet or higher) followed by a machine applied hard wax is more betterer......
Pretty much anything to help seal the surface is decent.
Granted, some wing profiles (PIK-20, SGS-1-35, etc.) don't really want wax since it causes water to bead which kills the L/D. Fly in rain, drop the gear......