I’m fortunate to have a lot of well-intentioned friends. They believe in a variety of noble causes and sincerely want to change the world for the better. To date, few of them have succeeded. 
With the terrible tragedy on Friday, we’ve seen an outpouring of good intentions on Facebook and Twitter. But I’d be very surprised if that sentiment produces any more meaningful change than all the similar outpourings following (far too many) previous tragedies.
Why? Because every failed movement fails in its own way, but every successful movement is alike.
There is really only essentially one way to create meaningful political change. I’m going to walk you through it now.
Step 1: Identify the decision-makers.
The USA is a democratic republic (not a democracy.) We have a legislature that makes laws, an executive that enforces laws and controls administrative agencies, and a judicial system that interprets the law and the constitution.
Nearly every aspect of our society is under the direct control of one of those branches (or its local equivalent) and no one else. If you want to change the law (for example to ban assault weapons), you must win over 51% of the legislature. 
Win over 51% of the legislature and you win. Win over 50% or less and you lose, no matter how much money you raised or awareness you created. It really is that simple.
Step 2: Identify your opponents.
The status quo is not random. Whatever aspect of society you identify as a bug, someone else sees as a feature. That person (or more often, that very large group of people) prefers things they way they are and will actively fight change. Sometimes, your opponent really will be a shadowy cabal of corporate SuperPAC’s. But in most cases your opponents will be an outright majority of your fellow citizens. In that case, you have very different problems that require very different tactics.
Step 3: Figure out how to sway the decision maker.
For example, let’s assume that you’re trying to pass a law; 51% of Americans oppose it; Congress voted down the law 41%/59% last year.
What are you to do? Since you’ve completed Steps 1&2, you already know that you need to pick up the votes of 10% of Congress, and that there is a large and organized group of citizens who are pushing Congress the other way.
What determines how a Congressman votes? A little bit of ideology and a whole lot of fear about reelection.
So you need to convince 10% of Congress that flipping to your side is the best way (or better yet the only way) to get reelected. You do that by identifying the Congressmen who won their last election by the smallest margins, preferably in districts where overall public opinion on your issue is as favorable as possible.
Step 4: Create a credible (political) threat.
Politics is the art of threatening with a smile. And now you know exactly which Congressmen to threaten.
You’re not going to be able to bluff this part. Politicians are incredibly savvy at reading the political winds, and if you’re just blowing air there is going to be a large opposition actively pointing that out.
You’re going to need to actually change a lot of hearts and minds, and make your target Congressmen painfully aware of that change. To do that, you’re going to need to get organized. You need to build an actual organization (with leaders and resources) that contacts citizens, convinces them, and commits them to expressing their newfound view directly to their representative. This effort has to be strategic. Getting a million New Yorkers to sign a petition for more mass transit funding is completely useless if the relevant bill is being filibustered by a senator from Idaho.
Step 5: Enjoy
If you follow these steps, one of two things will happen. Either you’ll realize that enough people disagree vehemently with your goals that you’ll never get what you want no matter what tactics you use. Or you’ll actually get to watch a law be passed that finally corrects a serious social blight.
This year’s successful war against SOPA is an excellent example of this method in action. That effort worked because the major tech organizations united in opposition to the law (which was already unpopular among those who knew about it), they put their message clearly in front of millions of voters, and they coordinated an outpouring of calls and letters to Congressmen. That groundswell made enough Congressmen realize that supporting SOPA threatened their own reelection, and the law collapsed.
I trust that my friends will remain well intentioned. And I look forward to all the wonderful things they’ll accomplish if they just remember: identify the decision makers, identify your opponents, figure out how to sway the decision makers, and create a credible political threat by contacting, convincing, and committing the right group of fellow citizens.
 Except perhaps on a very local scale, which is valuable but much less than they intended.
 Or 61%, thanks to our silly filibuster system.