Shut down your computer and disconnect the keyboard.
For a superficial cleaning, wipe the outer surface and the tops of keys with a lint-free cloth that's moistened with a mild solution of soap and water.
Turn the keyboard upside down and use compressed air to blow debris from in between the keys.
If you have sticky keys, or just want to perform a more thorough cleaning, you'll have to remove the keyboard keys. A key can be pried off of the keyboard by applying a gentle, even force to its bottom edge. Prying on both sides of a key at the same time works best. (Computer shops have special tools for removing keyboard keys, but a blunt object like the broken tip of a pencil should work fine.) caution
Almost all keyboards have removable keys, but some keys are sticker than others. Never apply too much force to a key; the key should pop off easily. Forcing a key may break the underlying fastener. Remove and clean one small section of the keyboard at a time. It's easy to lose track of what key goes where. If you want to remove all the keys at once, make a digital photo of the keyboard or use a second keyboard as a reassembly guide.
Clean the underlying surface with a Q-tip that's been moistened with a mild solution of soap and water. Dry thoroughly before reassembling.