Contact your representatives
We'll admit, it can seem sort of like a self-congratulatory exercise to send postcards or leave voicemails for reps, especially if they're already on the same side of the political spectrum as you are. But friends in government assure us that this, actually, is the best way to make a difference, and that they take response from constituents very, very seriously. Here's where you can find your senators, and here are your house members.
This small group of creative types is putting together monthly-ish potlucks where people share food and discuss how to make a difference.
This well-distributed guide about how to best resist also has a ton of links to small local groups doing everything from small things (yoga meet-ups) to big actions (march organizations), all close to your zip code.