Simple answer is as many times as you can find people stupid enough to use your dog when you have absolutely no idea about mating.
Complex answer is it depends on how old your dog is, and again, how many people would want to use him on their bitch, which would depend on whether he is Kennel Club registered, what you know about his pedigree and the dogs in it, whether he is a good specimen of his breed, whether he is hip scored and eye tested, if he is a proven stud, of suitable bloodlines for their bitch, of a good temperament and how much you are charging.
Stud dog owners also have a responsibility to the puppies they allow their dog to produce; could you be sure the owner of the bitch would be careful where they let their puppies go, and take them back if ever they needed to be rehomed by their owner?
Allowing your dog to be used at stud (not studed, that is when you put metal things into them with a stud gun) is not something to be taken lightly. Would you know how to handle a bitch in season if she was unwilling to stand for the dog, would you know how to help the dog mate the bitch if the bitch was trying to bite him/you/the owners?
What do you know about dogs tying, and how long would you leave it before intervening?
Please think long and hard about this, it is not a simple money making game and should really be left to people who know what they are doing and are doing it for the right reasons. If you still want to go ahead, the best person to advise you is the breeder of your dog, who may tell you reasons why the dog should or should not be bred from.
And before you ask, I do know what I am talking about.