The primary concerns with the pipe line and the risers are that they have not been damaged so they restrict flow and that risers stand upright so that sprinklers are properly oriented for operation. On a weekly basis, inspect and repair any leaking pipes or sprinklers, and reposition leaning risers. Watch for crashed or damaged pipes.
A sprinkler that is leaning a few degrees will distort the distribution pattern. Carrying a level during the inspection will help one to keep his/her perspective on what is vertical. If the ground slopes, then perpendicular to the ground is good.
Risers that are loose and move about should be staked and tied to hold them in place.