An often over looked aspect of making money is the art of selling. Sales skills are invaluable and should be trained and practiced by everyone. No matter what your line of work, or how you make your money, you are selling something.
Even if you are not directly selling a product, you are selling your time, your skills, or something. What is a resume if not a sales pitch for your product (you)? And the effectiveness with which you do this can be improved with the same skills that would help you sell anything else.
Once you are able to make the transition to working for yourself you will be even more directly involved in selling – affiliate sales, direct sales of your products, advertising, etc.
Some important principles to keep in mind with regards to selling: