I love that you are interested in this. Interest is the first place to start. I agree with the above link. I also wanted to include the oft forgotten art of writing your senators and representatives. This is even easier to do now with email, and as a future voter, your voice is highly important. I think most political officials would agree that they do not feel as connected to the younger generation of voters.
The best thing to do is to find a current topic that is actually of interest to you. You don't really even have to do much research to do this... honestly, watching the news or listening to NPR is a pretty quick way to start. Write a short, but carefully worded note doing one of the following: 1) thank him/her for voting a certain way on a bill of interest to you, and say why; 2) ask him/her to either support or not support a current bill or law on the floor; or 3) you can also simply say one or two issues that are important to you and why.
Of all the times I've written to my senators, I've actually received pretty timely responses.
I hope this helps. Bravo to you.
A book that might be of interest to you: The One Hour Activist by Christopher Kush (see link to Amazon below)