Most years, we have a driver and operator. In "arm" games like 2007, these roles have similar control demands and require excellent coordination between the two. This changes from game to game for us though, for instance 2009 was less operator intensive. In 2010, we really didn't use our operator much during the season at all. (In retrospect, we should have given them another official job.) The extra functions were relatively easy for our driver to control, but part of it was just lack of driver-operator coordination. Once we found an operator that fit in well, it got easier.
I'll vouch for the practice-practice-practice stances, though. Having been a
mechanical and pit captain, captain-manager, operator and coach, drive team practice is
the most efficient way to improve your performance. Don't change your drive team!
Also, Karthik says, 'the role of the field coach cannot be overstated'. If you don't know what you're doing, find out! Ask fellow coaches (especially if they're from 71, 1114, 148*, 217, 45, 33...) and
ask your drive team.
Read and practice.
*EDIT: yes, listen to that guy. ^