Two things hold true for being successful in sales. The first is having a system. A proven formula that if followed will lead you to a higher ratio of closed sales. Naturally, the system itself will vary from product and company. The main thing to remember is to find a system that has already been proven successful and follow it. Of course, you must also find a system that works for you, a system that fits your personality and does not infringe upon your values or beliefs.
From all of the great people that I have had the privilege to learn from, this idea was as consistent as the concept itself. Brian Tracy says if you want to be successful in any field, look for the people who are most successful in your industry, find out what they are doing and then do what they are doing / have done, and you should achieve the same or similar results. Sticking to the system is key, especially if it is one that has already been put into practice and has a history of positive results. Straying from a formula will usually produce unwanted results more often than not. This is not to say we should not look for ways to improve our systems, testing new ideas and techniques in controlled environments is vital for growth, as long as the fundamentals of the system are not sacrificed.
The other ideal that I believe leads to our success, not only in sales but in any profession or any area of our lives for that matter, is passion. We must have passion for what we do, we must believe in it in our hearts and souls. If we do not have that fire in us for what we are selling, we may have some temporary success, but we will never reach our true potential.