It's a good idea to get the "lineup" fixed early on in your group's life. Some venues/soundpeople want a diagram, before you go on as to where specific vocal mics, instrument mics, direct boxes, etc., need to be on stage. If you're doing pure acoustic, it helps to know where you're going to hear the harmonies, etc.

Sometimes it takes a rehearsal or two to work out just where everyone is the most comfortable, but once you get it set it really helps - there are no surprises when the chips are down !

In our case we have one lead singer on the left end of a semi-circle, so we can see her chord hand on the guitar. She plays a lot of major-minor songs and it can be a real chore to follow her newer songs if you can't see what she's doing.

In the middle we have our bass player/lead singer and lead guitar player/harmony singer who are husband and wife who need to hear each other.

I'm on the left end, singing and playing banjo. My only problem is that I hold my instrument neck more horizontal than most (eases hand/elbow strain) and if we're in really tight quarters I am almost poking the bass player in the ribs. But in the long run it works best this way.

Visually, this lineup helps since it is male-female-male-female -giving some variety. (It also helps that our two females are very attractive women - while we guys are kind of so-so!)

So - don't think of yourself as a prima dona - think of it as design and presentation.