Mark Markarian has a great post on how to effectively lobby Congress on animal issues. All I can add, as a former Legislative Correspondent and Legislative Assistant is to put in a good word for Medicare and Social Security. Creakers vote more then any other demographic group. You don't have to say you're old. Just give them the impression that you are. Make them work for the response instead of spitting out one form letter. If they don't answer your questions, call the local office and complain (in a nice way). You wrote on x, y and z, and they only answered x.
And another thing, if you want to know whats going on in congress, go to Thomas.gov. It's a great resource. Ask about their opinion on specific legislation. Ask them to co-sponsor bills you support.
OpenCRS is another great resource. The Congressional Research Service issues reports on everything from the political situation in Moldova to environmental policies related to hog farming. This is what members of congress rely on when they vote on issues. If OpenCRS doesn't have it, your local representative can actually get the report for you if you ask for it.