Maxima Bio-Wash or Muc-Off Nano Tech are great moto-specific cleaners to use. Meguiar's Wash and Wax waterless is also supposed to be safe for matte finishes, and I've used it on occasion for touch up washed all over the bike. The biggest things to avoid are 1. applying liquid or paste wax to the finish and 2. any product with a polishing element. Some spray protectants are fine after washing. Personally, I use Maxima SC1, as it makes the bike look great, and the finish seems to keep bugs and tar at bay.