Get your environment dialed in, no big temp changes, no high heat days, etc. There will be no argument with that, as environmental factors affect this as much as anything. IMO hydro typically yields more than soil, but i have seen 8 + oz plants out of soil.
Next decide do i want a lot of little plants, or a couple large plants? If you have 3 large plants you veg for 2 months they may yield more than 30 small plants but the small plants need little to no veg time. So you could take down 60 plants in the time you vegg and flower the 3 large.
If you are on a limited plant count a lot of us get a veg room set up so that we can always have plants in different stages, may not help actual yield but timing making it so the harvest is not all at once and then not again for 3 to 4 months (or longer).
Also Co2 will do no good if you are going to vent the room any how, it is meant for sealed rooms, since you will need the fans on while the lights are on the keep temps down, but the co2 only does any good while the lights are on.