Inspect filter screens for damage.
Clean the filter screens by opening the end of the filter and running water through briefly; if the screens have mineral build-up try soaking them in a 50/50 water and vinegar solution.
Flush the irrigation lines. To do this you must find the end cap and briefly run the system to flush out debris.
Check valve boxes for debris, build-up or muddy conditions indicating poor drainage and or a possible leak.