As other have mentioned, the biggest factors that influence yield ime
1.) Cultivar - this is the biggest imho. GG4 will ooze resin, a Haze probably wouldn’t. Try to find cultivars/breeders that are known for extraction or hash making.
2.) Moisture level of bud - you want this on the higher side. I like the throw a couple of fresh fan leaves in the jar with herb I’m going to press 24 or 48 hours ahead of time to re-hydrate the buds. You definitely want them more spongey feeling and less brittle.
3.) Pre-press mold - I yield better when I pre-press my bud into a mold. I use this one. I’ll pre-press with no heat. Then take the pre-pressed pucks and put them in the bags. Then place the puck/bag on the heated plates and increase the pressure just enough to start heating both sides of the puck. After heating for approximately 1 minute, slowly increase the pressure, pump by pump. Once you start seeing rosin ooze, you can experiment with the increasing pressure or just leaving as is to see how much will ooze out.
4.) Temperature - lower is better quality, higher temp - more yield.
You’ll get it dialed in and be overflowing with rosin in no time…