this is from what I have read.. so no personal experience with bettas...
Feed rich foods for about a week before putting together (assuming they are separated), and then put together with some floating plants (or none because they make bubble nests, the plants just help support the nest).
first and foremost you need to make sure that the male is ready
you know this when he is making buble nests.
next you make sure that the female is ready
she will have a spot on her stomach and will appear swollen.
then you let the female enter the males tank or bowl. but watch them carefully so he doesnt kill her.
take her out after 15-30 minutes.
then put her in the next day .
do this until you see the male "squeeze" the female, this causes here to release eggs.
Getting eggs is the easy part with bettas. Rearing the fry is much much harder.