Your male dog needs to be able to feel in the mood in order to be able to breed successfully. There are several things that you can do to increase his libido to make sure that he is ready and willing to get down to business.
Make sure his diet is a good one, with food that is made up of good ingredients such as meat products. He should always have access to fresh water and good exercise. A healthy dog will feel more like reproducing.
Give him a toy or a piece of material that has the female dog's scent on it. This will get him interested in the way that the female dog smells, and will help make him more ready for breeding.
Put him in the presence of the female dog that is in heat. Let him sniff her and begin the mating rituals.
Leave him alone with the female dog when she is in season. Keep a close eye on them, to make sure that there aren't any problems and to document any breeding that might occur. However, a male dog will have more libido if he is left alone in order to breed.
Take him away from the female dog, but still keep him close enough to smell her for 24 hours. This will keep him excited and ready to try again the following day.