The following is what I do. I will say here that you must be ready to "care" for the fry. Do you have microfood, know how to make infursoria, and have either brineshrimp eggs to make ready for hatching or microworms to feed the fry when they hatch? Bettas are different from your run of the mill fish and need certain requirements in order to have a successful spawn..
Note the egg tube, easy to see on these 2 females.
Condition the pair - feed well preferably live food and keep the water very clean.
"Breeding Tank" - small tank with approximately 4-5 inches of water, a corner sponge filter, submersible heater set at 80, a plastic lid or piece of styrofoam cup cut for the bubblenest and plastic plants so female can hide when needed. Do not have any rocks or substrate in this tank. Put the male in first. Let him get used to his surroundings for about an hour or so. Then introduce the female by putting her in a hurricane globe so the male can't get to her right away. They should show some interest in one another, and he should flare at her and start working on bubble nest. When the bubblenest is fair size, and she displays vertical stripes and stands "on her head" in the globe, you release her. As long as they are not sparing too badly, leave them alone. If one or the other is being torn up very much, they are not ready. Put her back in the globe. Some sparring will occur as this is the ritual of their mating but should not be permitted to last for great length of time. The process of the pair being ready can take from l hour to 4 or 5 days. When they are ready, he will "entice her to the nest and she will follow. The mating process can take anywhere from 1 hour to 4 or 5 hours. He will "embrace" her, squeeze the eggs out, and the eggs will fall to the floor. She will look like he has killed her, being very still and motionless for a few seconds. He will "catch" or pick up the eggs from the floor of the tank and "blow" into the bubble nest. (I had one pair that the male would not have anything to do with the eggs, and the female was the one who picked up eggs and put into the nest.)
When the spawning is complete, she will swim away from the male and "hide". He usually won't bother her as he is busy picking up eggs that fall from the nest. When spawning is done, remove her immediately as she may become interested in the "eggs" and start eating them. The eggs are white and are a little bigger than a grain of salt.
After the spawn and removing the female, you need to treat both she and the tank with the eggs with Maroyx. This prevents infection to her from any torn fins, and is needed in the breeding tank to keep fungus from developing in the eggs. You also need to cover the tank with plastic wrap or glass so that no "cooler" air is at the surface of the tank. When the fries' labyrinth starts to develop and they come to the surface for air, they can get pneumonia and die from the cooler air.
A cup of live baby brine shrimp. An excellent 2nd food for Betta fry.
Start an infursoria culture with lettuce and water or have on hand "microfood" to have something to feed the fry when they are ready. In about two weeks, you will need either live bbs or microworms to feed the fry.
At about 36 hours after the spawn, you will notice little "black dots" with tails falling out of the nest to the bottom of the tank. The male will studiously go to the bottom of the nest, retrieve the "fry" and "blow" them back into the nest. At first the fry will "live" off the yolk sac and do not need any food. I start to feed about 2 days after they hatch.
When the fry become a little more free swimming in the horizontal position, you can remove the male from the tank. It is also possible to remove him earlier if he is not a good caretaker, eating the fry. The fry will land on the bottom of the tank and be okay there until they become free swimming.
You need to keep their water clean during the time they are growing up. I use a very small plastic tube attached to air tubing to suck up the debris from the bottom of the tank. Suck the water into something clear so that you can look for and retrieve any fry that may have gotten sucked up the syphon. Catch with spoon and replace back in the tank. Water replacement "has" to be the same temp so as not to "chill" the fry and be dechlorinated.
In the weeks to come, you must pay close attention to the fry. As the males get older, you will notice them becoming aggressive with each other. This is when the males will need to be removed from the tank and "jarred". The females will be okay together. As time progresses and the fry become larger, you can add water to the tank to bring it up gradually to being full. If there are quite a few female fry, they may need to be moved to a larger tank so as to not overcrowd them. The fry are very slow growing. Even after almost 3 months, they are still very little. It takes months for them to develop any color or have any size to them.
You may notice that after removing the male, he "acts" weird. He may be very tired from protecting and retrieving the fry or even be "depressed" because his work is finished. Feed him well, add salt to his water and in a few days, he should be back on track.
You may also notice after a pair has spawned, that very shortly they are ready to go at it again. If you have the room and proper setup, you can repeat the spawning, however, you should wait at least 2 weeks if possible so as not to wear the pair out. Make sure that you have many "canning" jars cleaned and ready to separate the males. Raising bettas is time consuming but enjoyable. If you want a good spawn, the above should prove successful for you.