Berklee's Loudon Sterns looks at sidechain compression in the video below, particularly concerning track interaction. Don't have Ableton? Many of these tips can be done with Reason 6's sidechain input! Dig it:
"In this series, Berkleemusic.com facilitator Loudon Stearns covers five ways tracks can interact with audio effects using Ableton Live. The first installment, Sidechain Compression, shows how a compressor can be used to create an interaction between a synth and an acoustic bass part. The Post FX and Post mixer routing points are examined as well as compressor specifics.
You can study with Loudon Stearns at Berkleemusic.com in the Advanced Production with Ableton Live, and Composing and Producing Electronic Music courses." -Loudon Sterns