I am going to start this thread with a warning. Breeding Bettas is not for those without patience. It is very time consuming, and a very tedious process. It should also not be attempted by someone who is new to fish keeping, as it requires a lot of knowledge, research, and time.
Also be aware that I am writing this thread based on research. I have not personally bred Bettas yet, and everyone’s experience with it will differ. Some people will have issues, other will have a smooth breeding experience. Remember, patience is the key.
There are many steps you must take prior to breeding your Bettas. The first step is condition your pair. When breeders refer to conditioning, they are referring to the period of time, which is usually about two weeks, where they provide the best possible diet and housing conditions for their fish in hopes to prepare them for breeding. The diet is altered from the normal diet to enhance the health of the male, and to encourage the females to produce eggs. It is also for the pair to store energy so they can successfully mate, as well as so the male can sustain himself while taking care of the babies.
For the most successful breeding to occur, is is very important to condition the Bettas PRIOR to introducing them to the same tank. The spawning process can be very violent and it is very possible (although not uncommon) for one or both of them to acquire injuries. Conditioning your Bettas with clean water and high protein foods will help them gain the strength that will sustain them through the spawn, for the male rearing the youngins, and the female focusing on healing from any wounds suffered.
During the conditioning period, it is important to check your water parameters daily. Keep them temperature at a comfortable 78F (25.5). Increase your water changes to 2-3 times per week. Remove excess food. Monitor your pH and KH levels to ensure stability. Adding almonds leaves is advisable, but not required.
Focus on a nutritious diet. Increase the number of feedings to 2-3 times daily, but keep to small portions to avoid constipation or bloating. Be sure to introduce a variety of high protein foods. Variety insures a balanced diet. Live and frozen foods are the choice of most breeders during conditioning. Good choices of frozen or live foods include: (frozen) Brine shrimp, (frozen) daphnia, (frozen) glass worms, (frozen) mysis shrimp, (live)white worms, (live) grindal worms, (live)flightless or wingless fruit flies, and (live) black worms.
Near the end of the conditioning period, place the betas near each other so that they can see each other. This often stimulates the urge for reproduction. Signs that they are ready to spawn include: the female showing her breeding stripes, and may swell with eggs, the male will build a bubble nest. These are good signs that you are ready to begin the next step.
Credit for this information goes to: http://nippyfish.net/2011/03/09/conditioning-bettas-for-breeding/