It should be short, concise and polite. Discuss the policy or program and don t attack the personalities of those involved. Your letter should be typed, spell checked, grammatical and contain your name, address and daytime phone number.
Email is ok but doesn t always have the same impact.
Keep the letter to 150-200 words or less. It may be edited anyway and if it is too long it certainly will be cut down. Your most important point or points should be first. Your letter should describe how the issue at hand affects you or others like you. If a policy, practice or location is unfriendly to bikes say so and suggest improvements.