EFF Legislative Counsel Ernesto Falcon has posted an excellent, practical guide to talking to your member of Congress -- how to do it, how to maximize your efficiency, and why you should.
Lastly, one of the most powerful ways to talk to a member of Congress is to attend their townhall meetings and speak to them directly. These are usually hosted when Congress is not in session (see the calendar for 2017 here) and are announced through the member's online newsletter, which you can subscribe to by visiting their website. Townhalls are typically announced 1 to 3 days before they are hosted, so you need to be vigilant. Meeting with staff at the district office or in Washington, D.C., is valuable in conveying public opinion. Those can be set up at any time simply by calling the office (every office line is listed on their congressional website) and asking for a meeting. Just make sure you are calling the right office (go here to look up your House representatives. and go here for your senators) because, again, they will only want to hear from their constituents. For more information on how to set up and prepare for a meeting with a congressional staffer, see our page on contacting Congress.
How to Talk to Congress