In order to have a fair idea about the number of customers you will likely handle in order to make adequate arrangement for them and to ensure that the pool conveniently takes the student without their being overcrowded all prospective customers should preregister. Give them application forms to fill. You will change a token amount to cover administrative cost and stationery. Have the information for each customer record somewhere, say a register. If however you have a computer you can store it in it and thereafter you can do an analysis of these customers using such indicators as age, profession, prior experience etc.
You will have to develop your own system or techniques for attracting and arresting the interest of your students. Do not use force to make a student do or learn anything. On the other hand try to lure them. Especially in the case of children you can use such coaxing and luring things as game, toys, storytelling to get them interested. They learn faster and develop knee interest under such a conducive environment.
You can add great value to your private swimming instruction by producing a video which should contain all the necessary instructions on how to swim.