Here's an article I wrote BETTA BREEDING
Okay here's the deal with bettas, they can be deadly when breeding!
For breeding bettas here's what I would do:
Find a male and female fighters and supplement their diet with freeze dried and live foods for a few weeks. Get a 10 gallon tank And put a divider in it. Let them see each other. I used to use margarine lids to support the bubble nests. Heavily plant both sides of the tank, and hopefully the male will start to build the bubble nest. When all is ready remove the divider and let the begin to get to know each other . When the male is comfortable with the female he may invite her under is bubble nest. Be warned that they will fight and sometimes it can be fatal. He will begin to wrap himself around the female and ' quiver' . She will release the female and she will, fall to the bottom for a bit, then she'll go back for more. This can happen about 7 times depending on how old the pair are. He will collect the eggs and put them in the bubble nest. This is why you don't want any substrate as it will make it easier for the male to collect the eggs. After spawning the male will chase the female off and he will be protective of the nest. At this stage you should remove the female. Leave the male until the fry are free swimming. You will need an additional 2-3 gallon jars for the male fry and the females can stay in a 10-20 gallon tank. Don't keep the parents in the same tank as the fry. These fish can proberly lay from 50-400 eggs per spawn.