Bettas have different characters. Some make gigantic bubble nests while others never bother. When pairing my breeders, I DO NOT look for bubble nest. But I look at how they swim/flare. If they're flaring head on and holding their ground, they're most likely in fighting mode. But if they flare and swim all over the tank in a wriggly/"S" pattern (flirt swim), they're most likely in breeding mode. Both male and female must flare in this way - then you can breed them.
How to get them in a breeding mode -
1. Water - good general water parameter (temp., pH, etc) will make them healthy and instinctively they will want to spawn.
2. Food - a balanced diet will make them healthy and active. They (specially the male) will need the energy to spawn and rear the eggs and fry. Most males will not eat until his fry are free swimming. The spawning process may take a few days, eggs may hatch in 24-48 hours and become free swimming in another few days - it can total to over 7 days of fasting. During all that time the male will constantly be busy caring for his eggs and fry, gathering them and putting them back in his nesting area.
3. If you feel your male is of breeding age, healthy and active but still reluctant to breed. You can "force" breeding mode by flaring him for a much longer time. I generally flare my males for 15 - 30 minutes. So to get them into breeding mode I would flare them for an hour or more. This also applies for females.
Flaring them for that long a time often makes them stressed. Instead of getting them into breeding mode, you will compromise their immune system. So DO NOT totally open the dividers between their tanks. Just lift it 2.5 cm/1" , opening the bottom part only. They will not flare the whole 1 hour but they will be on alert the whole time. If they rest too long during this flaring period, DO NOT breed him. He is likely not healthy enough to be bred.
Do this once a day until he "flirt" swim during flaring. Them give him 1 day total rest and put him in the breeding tank the following day. He should remain in breeding mode...... you don't have to wait for him to make a bubble nest.