When selecting the different colored guppies, ensure you keep 1 male to 2 or 3 females. If you have 1 male to 1 female, the male guppy may harass the female. But with 2-3 females, its attention will be split, reducing the chances of harassment.
When setting the tank up, it is vital to provide spots where the fries can hide. Unfortunately, parent guppies sometimes eat their own offspring. But if the fries have places to take cover, most of them will survive.