If you have an air compressor, blow it off with that. If the dirt is just imbedded and not "stained" you can use a toothbrush and the air compressor and get most of it that way. Whatever is left should lift off by dabbing it with tape (like you get lint off clothes). If some elbow grease is needed with light moisture, water is best on a proper rag. Be careful with wipes....some are a great alternative, others like clorox could have chemicals that could damage your tweed.