All purpose gentle surface cleaner + good paper towels on most surfaces, including my mouse and a light brush over keycap surface. It's usually dust accumulating, so using a damp surface to collect it helps. I soak keycaps in unscented detergent every month or two, depending on when it seems like they get dirty enough. Mostly if there are particles of stuff on the desk they get brushed to the floor during cleaning, and I vacuum regularly.
That said, how dirty a desk (or any surface) gets is a function of 2 things, in my experience (as I clean 2 desks: mine and my significant other's):
1. do you eat at your desk? If you do, you probably will have a lot of food residue everywhere, unless you are very careful to not touch anything while you eat, and then take your plate away as soon as you're done. If this is the case, practice not eating at your desk or else don't touch anything on the desk while you eat and not until you wash your hands.
2. dust at home. In my previous 2 places, there was SO much dust to deal with, it was always a losing battle. One was from living next to a busy road with cars driving by all the time, and the other was from having a lot of old exposed brick walls with old mortar crumbling in fine powder over time (sealing the walls in clear protection coating helped somewhat for a while). Regular vacuuming helps somewhat.