Buy one of those cans of air. I can't remember what it's called. But it's literally a spray can that sprays a jet of air and blows out all the dust, dead skin, food and toenail clippings from your keyboard.
Or you could do what I did once and remove all the keys, clean the keyboard thoroughly, then forget which order the keys go back on!! I think I got the qwerty bit right and the numbers 1 to 9....
I agree with the paintbrush method. A new paintbrush kept specially for your computer is an ideal way to keep your keyboard clean. I give mine a one over nearly every day. I always keep it covered with a clean duster when not in use.
Most people don't know this but because there are no electical parts in the keyboard, it is fine to immerse it in water! So long as you make sure you get it dried out completely afterwards!