What I play onstage in any situation goes towards "How do I arrange my role for what is played onstage" The more musicians that are onstage means it is going to be harder to find a space for parts to keep the band from sounding like a train wreck. It does not mean I have to lay out in places, although that is a viable option to choose at times.
Accomplishing successful arrangements (especially on the fly) is called "The Art of Orchestration", and it involves first listening to everything around me above all else. These points are always on my mind:
1) Listen to the vocalist above everything.
2) Listen to the groove the bass and drums choose so I can pocket what I play accordingly.
3) Listen to the topic of the song to capture the emotion of what is said with my choice of fills, rhythms, or pads.
4) Play dynamically as shown in the free "Shenandoah" lesson.
5) Sometimes what we play to fit the song should be felt and not necessarily heard.
Listening to the other players tells me exactly what areas are available to explore...I never abandon the above points. For me, playing in a band requires mastering these points.