How do you set up your practice?

We are trying to find a new way to format our practice layout. Right now we have our JV practicing separate from our Varsity. JV will go offense while the Varsity goes defense then we will flip it. In the past we have split up our players to focus on one side of the ball. We would platoon our offense/defense as much as possible and the kids that play both sides of the ball would go through a crossover period at the end of the practice so they at least get some of the other side. Do any of you do anything different from either of those? We just want to try something new. Any ideas out there?