This is how I spawn my Bettas...
I'll start with letting you know that Betta breeding is extremely time consuming and very expensive....Even if you somehow ended up with 100 live fry and sold them all you would probably not end up even breaking even as far as profit goes....So before encountering this difficult task of breeding decide why it is you want to breed Bettas in the 1st place....
The 1st and probably most important step in a successful breeding is going to be your stock...I highly frown upon people who get this whim that they want to breed their pet store Bettas...The reason this doesn't usually work is because you know nothing about the age and the genetics behind these fish...It is risky and a waste of time and hard work....People do not want to pay for a Veiltail Betta and have it shipped at the tune of $31.00 for something they can find at a local pet store.....
OK, let's assume you have purchased some good stock from a reputable breeder and you are ready to go.....The most common mistake I've seen people make is their spawning set up...Somehow they think it is OK to breeder their new Bettas in a 10 gallon (or less) tank that Daddy has been living in.....It WON'T work! Trust me on this one! Betta fry are extremely fragile and need immaculate water conditions and they can not be raised in a tank with gravel......