There are many sites that offer the contact information to your individual lawmaker.
The National Education Association offers a brief article discussing writing an effective letter.
http://www.nea.org/lac/writing.html
State Legislator Contact Information –
Do an Internet search for your state’s information
US Senate Contact Link
http://www.senate.gov/general/contact_information/senators_cfm.cfm
US House of Representatives Contact Link
http://www.house.gov/writerep/