How do I breed guppy fish?

[MandyC]

I have had my guppies for a while and the females appeared to be pregnant. I seperated them off into a birth tank and over five weeks later still no babies. Sadly the three fish that I had died one by one until a week later, I had no more guppies. What happened? I' getting guppies soon for thier own tank. It has been almost two months since the deaths. What do I do wit my new female guppies to have life fish and healthy babies born? Please help!