I am raising my 1st batch of guppy fry right now. The mama fish, Lotus, was pregnant when I got her. I just bought a cheap little 3 gallon tank, and I bought a 5 gallon sponge filter off ebay for around 3 bucks. I had the little 3 gallon tank set up and running so that it would be ready for the babies. When Lotus looked ready to me, I put her in the breeding net. About a week later she gave birth to 10 tiny fry. (Actually, 11, but she ate one.) I moved the fry into the 3 gallon and fed them crushed flake food, and frozen brine shrimp. At a month old they were big enough to move into my kid's guppy tank with their 2 adult guppies.
Some people say that if you have java moss in your main tank, the babies will hide in it and some will survive. I might try that if my guppy had a bunch of fry, but since mine only had 10, I decided to save them all. I have also heard some people use floating plants for fry to hide in, but this is my first try raising guppy fry, so I don't know how well it works.
What kind\color guppies do you have? Is the mama close to giving birth? I have another guppy in the breeder net now that I am thinking will have babies soon! So exciting! Good luck. I hope this helps. If you can, please let me know what you decide to do and share your experience. I am always trying to learn more. Happy Fishkeeping!