Supporting the big groups like NRA, GOA, FPC etc are excellent but support is absolutely necessary at the state level. Considering searching and joining your local group. Iowa has become one of the most pro-2A states in the last decade thanks to Iowa Firearms Coalition and their supporters. The IFC is an all volunteer, all grassroots group consisting of many big names to include Mr. Pete Brownell himself. Check out the latest blog here

Here is a list of their legislative victories

Hawaii Firearms Coalition concurring here.  National orgs are great at national level stuff, but don't have the time or resources at the State level, a minimal effort.  State level orgs need funds and more importantly the manpower.  It takes thousands of people actively working to get things done.  Providing testimonies and attending rallys are great, but the more important stuff is taking coworkers and other people to the range, talking to non-gun owners, creating that professional relationship with your legislators, and mentoring others in 2A.

Something I tell people is "what is the absolute most you can do to protect the 2A?"