Which skimmers need to be opened or closed prior to attaching the hose to the vacuum?

As far as opening and closing nothing, just make sure your hose is filled with water it is eaiser to begin vacuuming, normally we attach the hose to the vacuum that goes in the pool then attach the hose to the skimmer then begin vacuuming if we do not loose our prime, if the pressure gauge on the filter is reading low you can probaly can start vacuuming if it is reading mid to high pressure it sometimes is best to backwash before vacuuming.