Guppy breeding not working?

I have a 20gal community tank with some different kinds of fish including 4 female guppies and 2 male guppies that I am trying to mate. They've been in there for about 1-2 months and I havent seen any mating or anything. I even got a breeder box to prepare! :( The temperature is at 73 or 74 and the water is very clean) Could anyone tell me how to make my guppy breeding a success? The lady at the petstore told me it was easy...:/