One way is to call your legislator's office.
Email is a second method.
Email is most effective if it is not a blanket mailing to all members, but a specific mail message to your representative or senator. When sending an email, remember to include your name, postal address and phone number. The best way to get a legislator's attention is with a short, well-reasoned letter. Identify the issue at the top of the letter and cover only one issue per letter. If you have more than one issue that needs to be addressed, write separate letters for each issue.