Be professional in both dress and manner. Don't say negative things about other legislators or public figures. Stick with one issue per call or letter. Information about more than one topic will only confuse the message and dilute your point. Consider yourself an information source.
Legislators have limited time, staff, and interest in any one issue.
They can't be as informed as they'd like on all the issues or even on the ones that concern you. You can fill the information gap. Encourage the policymaker to ask questions about your program or issue, then or later. Tell the truth. Know who else is on your side.