They never seemed to need anything out of the ordinary. SOme people say to add a little bit of salt. Mine bread constantly. (they are live bearers btw). I never did anything special. Water temp or nothing.
they are one of the few fish classified under "livebearing" fish. meaning there species do not breed and have there fry hatch from eggs, rather the fry are born alive from the mother.
keep the water at around 82 degrees (warmer water enduces breeding in fish).
and other than that you should be set. they are very easy to breed.