Hanging DryWall

On a 4X8 sheet of drywall hung horz. on standard 16" studs, what is the best quantity and placement of drywall screws?

according to code, screws need to be placed every 16 in. along each stud (for walls, screws in 1/2" drywall with studs 16" on center). of course, each end of the drywall sheet ends in the center of the stud so there is good support at each seam.