To breed bettas, for the first few days I place their tank next to one another with a divider. A few times a day I let them see one another for a few minutes each time. I feed them live food (black worms) about 3 times a day and as much as they will eat within a few minutes. Doing this will get them readily to breed.
Soon the male betta will start building a bubble nest and the female will be full of eggs with a white tip at the belly. This usually takes only a few days. Be careful not to do this for a long time, as the female may start to drop eggs.
After the male start to build a bubble nest and female are full of eggs with a white tip on her belly, you can then introduce them into the same tank. If using a smaller tank (smaller than 20 gallons), use a tank divider. Let the two counter each other. Once the male starts to attack the female, place the divider to keep them seperated. Try this for about 2-3 times a day. After a few days of trying, the female betta should start coming towards the bubble nest. Just remember to keep them seperated, if the male start to chase and attack the female. Eventually they will start breeding.
Make sure to keep feeding them during this time. Once they start to breed, stop with the feeding. After several countering the female will drop eggs. Most of the time the male will pick up the falling eggs and place them into the bubble nest. After they are done, the male will then chase the female away and then guard the eggs. Take out the female, as she my get kill by the male or eat the eggs.
After a few days the eggs will hatch and you'll have many fries. The male will try to catch them and spit them towards the nest. After a few days, the fries will start to be horizontal, then free swimming. Once a few start to swim about (little dashes), it's time to feed them. I personally use vinegar eel as they stay free swimming in the water, easy for the fries to see, and are cleaner to use. After a month or when they are big enough, move them to hatch baby brine shrimp, then to adult foods. After a few months separate females from males.
After most of the fries start free swimming, then it's time to take out the male betta. His job is done and he may also start to eat them if he isn't remove. Once you move the parents to their own tanks, you can start to feed them again. Feeding during spawning and while the male watches the eggs or fries, may make them want to eat the eggs.
A easier way to breed, is to use a larger tank. 20+ gallons and add plants for the female to hide, during introducing. This way you won't have to use a divider and also the female will have room to get away and hide from the male. The female will keep trying with the male, until they are successful. Just make sure to check the tank daily for signs of eggs. Once you see eggs, remove the female. Another thing, almond leaves also helps promote breeding, and helps to thicken the bubble nest, making it stronger. I use a small cut up square size cling wrap or a half cut styrofoam cup (cut vertically) and place it in the tank for the male betta to build the bubble nest under. It also helps to keep the bubble nest together. Also use a tank hood/cover to help keep air from breaking the bubble nest.
I know this is a lot of information. This is what works best for me when I used to breed bettas. Good luck.