Know why you are calling
Sounds obvious, but we have all been guilty of making a call just because it was on the list, having long since forgotten why we were calling. Or worse, never calling at all because you aren't sure of your reason.
Source: Business coach C.J. Hayden
Make it a habit to keep a note with each person's contact information about where you left off in your last contact and what is the appropriate next step.
The most productive calls are about something you know or suppose the other person wants from you, rather than something you want from them.