Never let the telephone ring more than twice before answering, and then answer in a warm, professional manner. A customer should never feel like they are an interruption to your job. They are the reason you have a job.
Document everything that happens in a telephone call, including the date, time, a description of the question, actions taken, and any needed follow-up. Keep information on file for any current customers.
Always follow-up with customers within 24 hours to make sure the issue was addressed. Even if you have no answer, touch base with them so they know what is going on. Remember that a happy customer can become a referral generator.