You elect them, you should also take the time to contact them. "They" are your US Senators and US Representative.
All federal officials have offices in their home districts as well as an office in Washington, DC.
A face-to-face meeting has the potential to have more impact than a letter; a letter, more than a phone call; a phone call, more than an e-mail.
It's important that the Congressman or staff member know that you are a constituent. All correspondence should contain your physical mailing address. Begin your letters with Dear Representative -LastName- or Dear Senator -LastName-.
Avoid boilerplate text. Communication has more impact if the words are yours, not those of some public affairs person assigned to generate a grassroots campaign. Use the prepared text as a guide only.
Be courteous, be brief (get to the point!), be specific.
House of Representatives
For details about your Representative -- including mailing address for the district and capitol offices -- use CongressMerge.com or Congress.org website services.
You can find the phone and office number of your US Representative on the House website: list by state; alphabetical list.
The House of Representatives also provides web-based "form mail" for all US Representatives.
The Senate website contains an alphabetical list of all Senators, with their capitol addresses and a link to their Senate website, which will have information about state offices and telephone numbers. It also has a link to the Senate's web/form mail for each Senator.