Here are three pointers that I gave one of the newer members to try as an exercise. The purpose? to widen vocabulary and improve confidence... in the end to make the music of the group sound better.
Set up a very simple phrase or repeated pattern. A couple of notes or chords will be enough. Use this a base to respond to. We got one of the group members to play it but it could be done on a loop pedal or a computer etc. Leave it going.
First: A useful technique to start with is to be able to copy or 'ape' the music that is already being made. Give particular focus to the rhythm. Try playing along exactly with what is being done. You don't have to make all the sounds in the backing but the ones you do make should be at exactly the same time as the ones in the backing. Get what you are playing to be indistinguishable - absolutely locked to it. It is adding timbral interest but not cluttering the music. Playing tight like this gives a lot of audio space in the music and can also make the rhythm sound powerful. It isn't what most people would do most of the time but it is a great tool to have. I find I use this 'identification' - particularly of rhythm - to build much more interesting phrases around.
Second: Leaving the backing going, make a distinct melody or short repeated phrase over it. This is much harder to do than some people think. Don't solo. Make clear notes - be heard. You may need to try a few phrases to get something that works. Don't worry about bum notes or 'mistakes' better to have those and get to something interesting. Don't 'bumble' - making indistinct chatter - audio clutter - that works but it isn't this exercise/technique :) Think Miles Davies - I'm going to come in, be heard and put a distinct phrase out there. TIP When you are practising sometimes singing or humming a melody before you come in is a good way to find something that really works for the music, as opposed to what you would normally play. If it is good you can then work with it - add notes, change notes, respond to it etc.
Third: Carrying on from this try addressing the backing phrase at different speeds. NB Use it as a stimulus rather than a straightjacket. Always being aware of the rhythmic stresses but allow yourself to do different things around and between them, even to ignore them when it feels right! Begin by playing a short, slow phrase - possibly just three or four notes, maybe the melody that you built in exercise two, then experiment with changing the speed of what you are playing. Could you double the speed of the whole phrase? Could you half it? Could you start off slow then change the pace up mid phrase? TIP Avoid long periods of playing at the same speed. Again this can be used but its not what you are going for in this exercise. As we ran this exercise I found that new emphases presented themselves. Leading the music to new places.
Listen out for these kind of techniques in other people's playing. How do they do it? NB They are difficult to write about but much easier to play. Respond to them in your own way.
Jerry Goodman's violin on this clip is a good example albeit within solo'ing.