For a light clean you will need an old, small, dry paint brush with good clean bristles, some newspaper to catch the debris, and a damp lint free cloth. The cloth could be damp with water, or a very light mix of water and washing up liquid. No strong detergents or bleaches. With the PC powered down and the keyboard unplugged start with the brush and clean between the keys. Holding the keyboard upside down and shaking and tapping after brushing should get most of the debris out. Now the keys can be cleaned with the damp cloth.

Wrong Way To Clean A Keyboard

Medium cleaning involves the use of a can of compressed and isopropyl alcohol. Having used the brush to loosen debris you can blow it out using the compressed air and then proceed to cleaning the keys with the alcohol. Cotton buds could be used to clean a little deeper but take care not to soak the bud. The work with the air can is best conducted outside.

The last method would involve prying the keys off the keyboard to expose the chassis and cleaning from there. If you are going to do this you need to be sure that you know the position the keys came from and be sure that you can successfully replace the keys after removal and cleaning. As you can see this method is pretty involved, hence... Maybe it's time for a new keyboard.

Finally, for safety reasons, please be sure to empty the can of compressed air when you have finished using it, even if you have to hold the the button down for five minutes to do so. Do not leave any air or propellant in the can.