I think the answer to this question depends entirely on what you've got as a source and where you want to go with it. Pretty vague, I know, but there is no real system for exactly what's going to work every time when you're compressing bass or anything else for that matter.
Push the parameters to the extreme to hear exactly how this particular knob affects the sound of the song... then roll back until it sounds "normal". Do this a few times, with your eyes closed. I find it's too easy to roll back to a number that looks good, instead of one that sounds good. Make sure to hear these new settings at both the quietest and loudest parts of the song to make sure the extremes in the waveform patterns don't sound weird. Sometimes compression will sound pretty odd in the loud parts where the quiet parts sound fine.
