Most any good all purpose cleaner will do the job. EFHI, Meguiars APC+, even diluted Simple Green all work fine. Use a wash mitt or a soft bristled brush for scrubbing. You want to get the dirt out of the textured pores but don't want to mar the plastic in the process.
For protection you can use the same stuff you apply to tires as long as its not silicone oil based. If you use stuff like 303 Aerospace or Vinylex, you're good to go. Water based protectants don't have great durability but they're plenty safe.
There have been a few threads about plastic cladding and molding in the past so you may want to use the Search function and look for them to view other tips and tricks.
