go to your local LFS, look at the Mollys and Platys. The ones that have large plump stomachs are most likely already pregnant. Check the under side for a small barb like deal, a different color then its fins that will be a male. The others that look kinda plump are probably close, my most recent fry of Molly literally was born 4 days after i got the fish from the LFS. Just get a breeder box that suctions on the side of your tank, and put the plump looking females in there, if they dont do anything wait a few days, then put em back in for a day, and keep doing this until they fry. The fry will hide in the bottom of the feeder box and can grow to a decent size in it so they wont be eaten by the parents, then you can let em loose with the parents without much worry of the parents eating them, I only started this recently and have had 4 frys so far, breeding them as feeders for my red wolf fish, bichir and peacock bass. Its quite easy with these live bearers. Also they may have a dark spot near where youd imagine baby fish come out of called the gravid spot, another hint to pregnancy.