I do vote. I have a hard time convincing myself that it's even worth the time it takes to do so, but I do it.
I've tried writing to my representatives to express my views. I get form letters in response, with absolutely no indication that my voice has been taken into account in even the smallest way.
People say you should get involved in local party meetings and such, but there are no viable parties that I agree with even remotely, and in any case I'd rather stab myself in the eyeballs with a toothpick than attend such meetings.