Freq Out
A good practice exercise is to go through the many waves available and try out the sounds in extreme-frequency situations--very low or very high, or very much NOT where they were originally intended to sit. Try doubling "normal" sounds with these extremities, and putting the result through some heavy effects. I can ALWAYS find something really cool this way. Use the high-freq items as transient additions, giving them real-short sustains and quick attacks. Since the human brain 'identifies' a sound primarily from it's attack envelope, you will be experiencing some radical changes on sounds you thought you were 'used to' with this technique. This is amazingly effective in giving definition in a mix to a bass instrument.
Extremely low varieties of a wave often like to be treated with some kind of rolling vibrato effect, yet a very fast vibrato effect will give an impression like a nice, loose bass drum when coupled with the right attack transients. Thunders and rumbles and gigantic explosions like you've never heard before live "down there" for a huge number of waves. (Check out 'White Noise.') If your windows rattle, you're on the right track! :-)