I have had yellow cichlids for maybe 2 years enough for them to have I don't know how may batches of babies. When I first got them they were about 1.5 inches long and I picked them based on coloring and that they followed each other around the tank...
I guess I was lucky because in about a year when they reached maturity they started having babies and are still having babies. I later bought some Aceis (blue) cichlids. I picked them out based on color/markings and they were following each other around the tank.. Again I was lucky and when they reached maturity they started having babies...
I just bought some jewel cichlids, I think I picked male and female but I will have to wait for maturity and babies so I will know I picked right.
I do a lot of reading about the fish before I buy them. I read on many web sites about male and female for that type of fish.