When you start a new customer relationship, sit down and make a "wish list" - all the concerns and needs the customer is facing that you might solve. From this, develop a checklist. Every time you make a sales call on that customer, review the list together. See how many things you have accomplished, discuss what's in progress and, of course, add to the list. This makes you and the customer teammates in accomplishing goals - and gives you a reason to call back.
