This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
First, if you do not have a picture of the keyboard, it's a good idea to make a diagram of key locations. If the keyboard is a separate unit, remove the keyboard cover-- i.e. the 'shell' that surrounds the keys. Spritz it with a cleaner (like Windex, Fantastik, etc.), wipe, and let soak in warm soapy water. What you need to do next is pull the key tops. A puller tool which lets you get around and under a key on two sides is very helpful; or, you can use fingers and a small screwdriver or leter opener to pop off the key tops. For SPACE and other large keys, take care to unhook stabilizer bars and pay attention to how the bar for each is connected. Spritz each key top with Windex, Fantastik, etc., wipe, and let soak in warm soapy water. The letters, numbers, etc. on key tops are, usually, solid plastic and should not be in any danger of getting wiped off. For sure, you would not want to use any petroleum distillate or other solvent which attacks plastic for cleaning. Everything is rinsed, blotted with paper towels, and allowed a couple hours to dry. Once the KB interior is de-dusted you can blot away remaining moisture from key tops, etc. and put everything together. Install the large key tops with stabilizer bars first, then press on the others. If the keyboard is a separate unit, wipe/clean the cable. -----------------------------