I am doing website design seller for over one, There are some tip I get from my experience.
1) Join in a competitive company who any design website very well.
2) Have a good relationship with designer.
3) Advertisement (Emailing, Calling)
4) Call back once the customer showed you they want to do a website.
5) Approach to customer closely
6) Always ask what they want, and help customer what is the best solution for them
7) During the project, keeping in touch with your customer.