Remove a key or two by lifting them off. Use a can of compressed air to blow between the keys aiming at the ones you removed. Then put the keys back on. Of course you will want the computer off when you do this, and don't shake the can of air before using. You can use rubbing alcohol and Q-tips to clean the keys and in between them as well.
A vacuum with a brush to gently dislodge any bits of crud will also help.
I am hoping you are smart enough to NOT follow the advice of taking it outside and hosing it with a pressure washer.