Well that depends on tires, and riding type that I am going to do, ext... Sag is a general setting and I always set it first. Then move onto more performance setting (rebound, compression, preload)
Set on the bike with your gear on. Jump around on it, let it settle. Have someone measure from the frame to the floor around the back of the motor. Then around the front of the motor. Then get off the bike slowly. Measure it again. This is Sag. You can set both front and rear from this point.
hard core trails, I limit sag to about 2" max, dunes I set it up around 3. Trails my ride hight was normally Rear 7 1/2" 20" tire, front 7 3/4" 21" front. I set it up this way running Fox Evols, according to Fox.