Start by reading the Indivisible Guide - a very helpful document written by former Congressional staffers that lays out a step by step outline for how you can take back control of our government. It uses the Tea Party as an example.
Then read this short piece in the New York Times that explains why picking up the phone to call your elected officials is so much more powerful than emailing then or writing a letter.
If you're intimidated by making phone calls, you might benefit from reading Emily Ellsworth's guide, Call the Halls.
Then watch this short interview in which Michael Moore outlines his 5-point plan for 2017.