[QUOTE=
And when you say "try to support what he is playing", do you mean if the solo is in C Major, I should play something in C Major too?[/QUOTE]
What I meant by supporting the soloist is playing something that complements what he is playing, more in tonality than in any particular key. In other words, try not to play something similar in tone , otherwise unless you are completely in sync with him, it will sound bad.
The job of a supporting player (and that is everyone's job when someone is soloing), is to lay a nice foundation. If everyone did the same thing (or always accented the same beat), it would sound monotonous.
I've been playing a long time, and I still have jams where at one point everyone just gels together, and there is magic in the air. Its for those moments that I live for, and only players that have experienced it can testify to this. Its like musical nirvana. I've had tears in my eyes at times, so powerful were the emotions. Just watch videos of players like Jimmy Page, Carlos Santana, Gary Moore and you'll see what I mean.