Avoid stress

Plants under stress slow their growth and inhibit flowering and production. Stress is caused by trauma caused by growers. Withholding water, changes in photoperiods, low light, nutrient deficiencies or toxicities, wrong temperature, wrong humidity, bugs disease, excessive or incorrect pruning --- all these can cause problems
Stress can also cause hermaphrodites. This is when a portion of the female plant changes into a pollen-producing branch. Usually caused by light introduction during the dark period, it can also occur when stress is excessive. Unless caught, this branch will pollenate itself and all surrounding females. For breeding purposes, this is counterproductive, since the genetic material is from the same plant. Seeds produced in this manner result in plants that are more likely to be female, but are also more genetically predisposed to becoming hermaphrodites.
Remove hermaphroditic branches ASAP, and figure out what caused this problem. Correct it immediately, or you could wind up with more pollenating males than are necessary. Plants with perfect flowers, such as tomates and peppers, never have this problem, since both the male and the female parts are contained within each flower.