The most common mistake made by sales people tends to be,  speaking more than listening during a sales call.

When calling customers, asking open ended questions should be a vital part of the call, to gain information and to use in overcoming objections.  When receiving answers to questions, be sure to pause for a few seconds, making sure never to interrupt, and allow the potential customer continue speaking, in case they may be thinking of what to say next. Once sure the customer has stopped talking, then respond accordingly, continuing to ask open ended questions to acquire more information to ascertain their needs and how to match your services with their requirements.

Remember you have 2 ears and 1 mouth, use them accordingly.