Never use threats. If a bill presents what you feel is the wrong solution to a problem, try to propose alternatives. Take a clear position and ask your legislator to state his or her position. Try to time your letter when the bill is in subcommittee or full committee hearings before it is sent to the floor for a final vote. Form letters are out.
Personal communications are much more effective.
Keep track of what happens. Don't forget to write to thank your legislator for favorable actions - this will help create a good atmosphere for your next communication. If you disagree with a vote, let your legislator know but keep points 4 and 5 in mind.