I just happen to breed rainbows, so I'll share my experience with you! Rainbows are egg layers as you probably know. They lay their eggs in moss or live plants. To collect the eggs, place a mop made from synthetic yarn in with the parent fish (more females to males with max of 3 males.) A separate bare breeding tank is preferable than the community tank. Feed the fish a varied diet including live and frozen foods starting 2 weeks before you want to breed them.
After a few days, pull the mop and see of you see any tiny clear eggs (they look like glass beads.) Once you have the quantity of eggs you need, pull the mop and place it in a 5 or 10 gallon aquarium heated to 82F along with a sponge filter set on a very slow stream of air bubbles (2 to 3 a second works fine.) In a few days you should see fry at the top of the water. The fry should be fed live foods initially. Foods suitable for feeding fry this tiny include vinegar eels, micro worms, and insuforia.
That's the basics behind rainbow breeding. If you have any more questions about it, pm me and I'll do my best to answer!
