After learning the basics about compressors (see Compressors 101 earlier blog entry), then you can use this general guide of the type of overall effect you are going for.
If you want a Natural sound (the compressor is not noticeable):
Use a slower attack (longer than 75 ms) and gentle ratios (less than 2:1). Always allow the compressor to "relax" back to zero several times a measure.
For a Punchy Response:
For a harder, punchier sound, use higher ratios and thresholds, but keep an ear out for any distortion.
If you want a Thick and Dense sound:
For a thicker, denser sound use faster attacks, medium ratios, and lower thresholds. There will be much more gain reduction though.
If you want a Pumping Effect:
For an overstated pumping effect use fast attacks, high ratios, and a longer release time.
DO - Avoid using extreme settings to begin with. This is especially true if you are just trying to control the dynamics.
DON'T - Add compressors to every channel just because you think you're supposed to! Start with minimal compression and carefully choose where, when and why to add a compressor.
DO - Experiment with different kinds of compressors. There can be some big differences!
DON'T - Don't forget to bypass the compressor occasionally to check that you're getting good results.
DO - Remember to balance the output gain so the level doesn't change when you engage the bypass. In other words the before and after volume level should be the same. We hardly ever use compression without changing the output makeup gain. If you add 3 dB of gain reduction (GR), then you should be able to add 3 dB or so of make up gain for the output.
DON'T - Don't be afraid to experiment. Some of the greatest sounds in the history of recorded music came from misused and abused compressors!
Next blog about compressors I will talk about the "Knee" of a compressor! I really do hope this helps. It helped me in the beginning!
As always - Make it a GREAT day!