The best way to close a sale is to have completed the four steps, before the close is attempted. Those steps are: introduction, investigation of customer needs, presentation of service, validation (confidence building).
If you try to close a sale without first having done the necessary steps, you will almost certainly fail.
If you successfully complete all of the steps, then closing the sale will be the natural progression of the transaction. They may even ask you, how they can purchase your product.