As a guppy breeder,
whether you consider yourself a beginner or a master breeder,
you should try to adopt
two specific goals into your breeding program.
First, breed for consistency
Secondly, work out a feeding program
that will help to improve the size of your fish.

Hatching Brine Shrimp by Igor D.

Raising fry on live or frozen Baby Brine Shrimp,
live microworms, egg yolk, etc. will build them up quickly
to take on an even greater variety of food
when they are physically able to consume it.

Microworms by Igor D.

Live food is known as the best food for fish
since its nutrition is fresh,
it provides essential fats and amino acids,
it survives in the tank so it rarely fouls the water,
and fish enjoy eating it.
Live cultures are rarely sold by stores,
but can be obtained through aquarium club members,
fish auctions, and via the internet.

Freeze-dried foods are a close second nutrionally.
The food is frozen, the moisture is evaporated,
and the nutrients are preserved.
Freeze dried foods can be stored indefinitely in a cool, dry place.

Flakes are about as good as freeze dried foods,
and in many cases,
better in my opinion when there is a good mix of ingredients and vitamins.
The key to remember, though, is variety.