So often, almost every time in fact, when I'm playing some songs in a song circle etc. there is almost always one guy with a "look at me" approach to being a back up guy. You know the type - the hot shot guitar player that has to run leads all over the verse and chorus and bridge and then expects an extended solo to complete his performance. The worst case is when someone comes in with the ramrod approach but totally doesn't know the song and for some reason doesn't think about listening first to see what's happening! This is totally not what it's about. Whoever is singing the song is the star of the moment and the guy should be a back up not a forefront! If there's a guy like this in the circle, it makes me want to go home. If I'm in a camp situation, I will sometimes get up and travel around to a spot where each person in the cirlcle is playing a song and the other folks are listening and NOBODY'S jamming!
I often play some sax with various singer songwriters or bands. Most sax players will start right in on the intro playing lick after lick and finding every space to put in a fill. My formula, if there is such thing, is to wait until the second verse at least to come in. Then I play about every other fill, a little solo, then drop out until the end. I try to focus on the main person singing and hopefully add to it rather than take attention away and draw it on myself.
If you are a back up guy, everyone will like you better if you start off by playing HALF of what you think you should play, then take out a little more. Listen to the lyrics and SUPPORT the singer!