I get this question a lot. After running into a mouse nest this week, I've decided it's time for some coaching on how to keep your instruments clean, and maybe some preventatives on the mice situation. I'm a squeamish technician, not a exterminator, people.
Dusting the outside is self-explanitory. Don't use a ton of wood furniture spray polish stuff (especially Pledge). It just makes the case kind of gunky, and ironically, attracts even more dust.
You can clean your keys with a damp washcloth. The magic substance I bring in the unmarked bottle for cleaning keys is H2O. Make sure you get the sides of the black keys, and get all the dust on those last four notes on each end! There's really not much excuse for this...
Now for the inside.
If you've put together a piece of IKEA furniture, you got this.
The lid on top of the piano opens up. The front can come off, and the bottom piece under the keybed comes off as well. The bottom is easy, the top will either involve a little hinge on the inside, or a screw. You can figure it out! Your disassembled piano should look something like this:
Get that vacuum extension and go to town!
Here's a caveat to people buying used instruments: If the current owner says casually, "It was in the garage for just a little while and then we moved it back inside," YOU NEED TO OPEN IT AND CLEAN IT BEFORE IT ENTERS YOUR HOME.
Putting a wooden case full of soft felt and leather in the garage is essentially putting Little Critter's dream home on the real estate market with a “free” sign on it.
Thank you for helping me make the world a better place, one shiny, dust-and-critter-free piano at a time.