I would have to say that I take the smart way out and DON'T breed bettas. First of all do you have 1) a breeding tank of at least 10 gallons seperate from the one you have the fish in now; 2) a hospital/recuperation tank for the female after spawning (at least 5 gallons); 3) a 55 gallon tank to allow the room for the little females to grow up until they are ready to be sold/given away; 4) bunches of small containers for the male fry to go into when it becomes obvious that they are male so they won't kill each other. All of these have to be fully cycled and of the cleanest character AT ALL TIMES, including all the small containers or the fry will be deformed and the fins will not form normally. This means DAILY water changes of at least 50% on ALL of the containers and constant water testing. You also have to have good temperature control through all this. Now I do not know how the professionals take care of heating all those little containers, but I do know you cannot just let the room temperature do the job as there would be too much fluctuation. Now, please do not give me the argument that they are kept in the petstores in unheated containers. Those are not fry they are grown fish. Fry are still forming fins and bodies and have to have PERFECT water/temperature conditions to develop into beautiful fish. To breed bettas takes MUCH work and more EXPENSIVE equipment. Unless you are planning on opening and running an operation to do this as a profession or you are independently wealthy and can afford to buy anything you need and hire help, I wouldn't consider it if I were you.
One other bit of information, I am not saying all but MOST of the Bettas sold in petstores are past breeding age and even if you introduced them they would probably not spawn. What ever you do though DO NOT just put a female into the tank with a male. Getting them ready to breed means a special diet and conditions for days or weeks ahead of time. I would suggest that if you do not know how to do it yet and are determined to continue that you HURRY to the public library and get the biggest book you can find all about what you need to do to get them ready to breed and read it thoroughly. You may do what you will but I am totally against amateurs breeding one of the most difficult fish there must be to get set up to breed. One more thing, there is a very real possibility of losing or injuring one or both of your breeding pair if you do introduce them at the wrong time and they are not ready to "be nice". They can and will hurt each other.
About all I can add to this is,from what I've read, you should always add the male to the female's tank and never the other way around...I'm guessing that's because the male of most species,when put in a new environment,are more likely to revert to natural instincts and mate,rather than behave territorial.
Sorry it doesn't work that way with a Betta as the male is the one who has to build the nest and he has to do that before the female is brought into contact with him. This is one of the reasons it is NOT advisable for amateurs to breed them. The regular rules do not apply to Bettas, the rule book goes out the window and they are a whole new ballgame. He stays around afterward for a while and tends the nest but not too long or there will be no fry to raise. This is not a feat for the faint of heart.
Yeah, about most bettas from the pet store being to old, I think I had that cos I did everything I needed to and they still wouldnt breed, I went and spend loads on extra tanks, months cycling them and preparing them and all for a waste! My father-in-law breeds bettas, after his first spawn that I still dont know how it happened cos he hadnt prepared correctly for it. He now spends his whole day tending to them, its a full time job! It really is! Hes spent thousands on his bettas and is very succesful with them but also suggested I dont try until ive got more time on my hands, and know more about what im doing, so hes teaching me at the moment...
Or, you can use a divider between them, until the male builds his bubble nest. Then all you have to do is lift the divider and introduce the female to the male. Its true tho, unless you don't work and have ALOT of time. I wouldn't recommend this, its ALOT of responsibility.
I am afraid that would not work either. They would have each other so stressed that they would die of the stress. They should not even be within eyeshot of each other until they have had weeks of preparation including special diets and conditions in the tanks. This really is a big job and there are no short-cuts.