Be honest, present the political downside as well as the positive. Provide information for legislators to use in responding to opponents. Analyze your opponents position and attempt to neutralize it. This analysis is as important as your own case. Develop allies by speaking in community forums and asking for support.
Coalitions always work best.
Understand the current legislative context, i.e., other issues, distractions, etc. Identify the issue in terms of substance and political affect. Do not offer opinions on issues outside your direct concern. If you do not know an answer, you can respond in a follow-up letter or phone call. Do not base your arguments on emotions.