Air Attack orbits highest over the fire. As tankers arrive, they will be placed in a lower orbit until air attack calls them in for a drop. Air Attack oribits opposite direction of the tankers in order to have twice the visual on those planes. Copters scoot close to the ground between their drops and their source of water (called a "pond"). They will typically stay off the fire while a tanker is in the process of dropping.
On a bigger fire with plenty of tankers and helicopters the two may be fighting totally seperate lines of the fire and not have to worry about each other. This diagram shows the cross section of the orbits and how everybody stays out of the way. Next time you are on a fire look up and watch them all circle around at different elevations. And over the radio, using this diagram will help you visualize what you are hearing as everybody talks away.
Enjoy my elementary crude diagram made 5 years ago :)