Be accurate and thoroughly knowledgeable about the subject discussed.
Legislators are extremely busy people, especially during session.
Make it clear who you represent, what you want to talk about, what your position is, and what you want done. Show how the issue relates to his constituents or committee responsibilities. Make him aware of opposing viewpoints and potential political liabilities if your view is accepted. Heavy-handed tactics just don't work and any threat of retaliation could well backfire. Also, losing gracefully on one issue can build credibility and friendship to help on the next one.