give them fertilzer with a high middle value (N-P-K) use (12-55-6) That promotes flowering, I use superbloom, it comes in a big jug and is at lowes/home depot for $10. Light is the number factor in growing but just get the plants as close to the light source as possible without damaging the plants. At four weeks you should have bud formation going on and make sure you kill the males or keep em seprated. If you don't have a lot of buds think about trimming away lower branches that get little light so the plant can focus on the tops of the buds. Then around harvest take the tops first and then give the middle portion more light, basically harvest in stages.Good luck.