A touch of rubbing alcohol mixed in water is the best way to go. The alcohol will evaporate and it leaves no residue at all (no matter what you use, it CANNOT be anything oil based), and it will cut through any oils or grease. Use a microfiber cloth if you have one, cotton balls or qtips can leave crud. Most electronics cleaners and screen cleaners are nothing more than a bit of isopropyl alcohol diluted in water. A whole bottle can be had for about a buck and will last for years. Aside from that, compressed air to blow out the dust. Though for removable plastic parts like faders, you could put them in a dishwasher, just give everything a while to dry COMPLETELY.
It's safe enough that I've used it to clean thermal grease off of CPUs and never had a single problem at all. Also if you drink a lot of water like I do, don't leave your cleaning solution in a glass laying about. I've almost drank it more times than I can count.