A mistake i made early on is cramming too many or too big of plants together. Its best to fill te room, but leave each plant room to grow. For me, growing in an ebba nd grow, i found 8 plants, veg for just under a month, filling in about 1/3 of the overall space is perfect. Use clones, all the same strain. Grow it a few times to dial in to exactly what it likes to be fed. ALso, get a good yeilding strain. Make sure all conditions are ideal and keep at it. From what i have seen, yeild will come with experience. WHen i first started, i would have huge mistakes and errors, and my yeild sucked. The better you get, the more you get a feel for everything, the greater yeild you will acheive. No secrets, just doing everything correctly with a high yeilding strain under the ideal conditions. Dont focus your energy on expensive supplements and what not until you dial in all the basics. Remember your single limiting factor will throw off the entire balance.