Watch the Blues for Two online guitar lesson by Mimi Fox from Jazz Performance
I have to confess that this is something that I had to learn the hard way! (After having some great bass players glare at me!). Here is an example of where less is truly more! When you are playing with someone for the first time, try playing some quiet and sparse chordal punches and see how it feels and sounds. Most importantly, ask your fellow musicians if your comping feels good to them! Don't be afraid to ask! It's always better to have someone say to you: "Sounds great, but don't be so shy about your comping behind me give me some more to play off of "rather than:" You sound like a locomotive running over a lamb! "