Become a laywer, get a case, get it accepted by the supremes and argue your case in from of the USSC
Sorry, I could not resist.
Or you could help fund people like Alan Gura who was the lead laywer in Heller and is lead laywer in McDonald.
http://en.wikipedia.org/wiki/Alan_Gura by supporting him and others like him that are already fighting the current legal morass.
Please note that Mr Gura is NOT supported by the NRA, they have a rather "interesting" history, but rather by a libertarian minded individual who last I heard did not even own a firearm. I mention this because there are many ways to help cause change and that the nonmainstream approach of many of smaller groups ( RKBS, SAF, JPFO, etc...),that are IMHO on the cutting edge on firearms law, desperately need funding help. There are many groups besides the NRA that need support.
Another avenue and also needed is political action, please note I did not say voting. Voting is taking 1 hour on average once a year, politcal action is writing letters, talking to your politician, helping your politician by donating time and/or money, showing up for rallies, lobbying etc.....
Lastly be good PR for gun owners, the public and the Anti's judge all firearms owners by the behavior of the wackiest gun owner they know is a gun owner .
Warning, you have probably heard of the death of a thousand cuts, fighting for a legal change is more like the fight of 100,000 spit balls, very messy, very annoying, very very very long.
Welcome to the fight.
Best wishes
NukemJim
PS If you are intersted in full-auto legal history you might want to check out the Hughes ammendment to FOPA and the NRA response to the ammendment.NJ