If you want to strengthen your clairaudience, try to go to bed a little bit earlier than you normally would. Dance on the edge of sleep.
But don't fall asleep. When you're in a very relaxed and meditative state (that's not quite sleep, and not quite meditation) it's easier than ever for clairaudient messages to reach you. Listen for voices, music, and other strange sounds. With practice, you'll begin to recognize the difference between physical world sounds and spiritual world sounds, and put yourself into that meditative state more easily, and on command!