You also need to be a professional salesperson. Read books and attend seminars on how to sell. Do role playing and practice your selling skills. When you don't get the job, call the customer and ask why. If the customer decided money was short and the job couldn't be completed now, stay in touch.
Most contractors quit after the second call.
Once you've completed the job, stay in touch by either direct mail or a phone call. If you did an exterior job, you'll have the inside track on interior work. Additionally, you may be recommended to a neighbor or a relative. Larry Fuchs sends thank-you notes, sometimes a July 4th message, or a form letter on quality stationery if he drives by a previous job and sees the place needs his services again. Certification indicates specific contractors are performing at a certain level, and maintaining their businesses at a professional level.