Is a call you make to yourself.
Doesn't matter what the product or service is -- yourself, a computer, daily dog walking. You must be 100% convinced that what you have to offer is worth the price, and that the person you're calling next actually would benefit from having it.
When you're 1) fully convinced and 2) able to transfer that convinced-ness to others, the following will happen: hands get shaken, people say "Yes", and sales come in.

Everything from there is pretty easy.