As I've argued before, the best way to fight negative stereotypes is for people unfairly subject to the negative stereotype to use in-group peer pressure to raise the bar. In short: "Stop making me look bad!" Over at Agoraphilia, Glen Whitman offers an eloquent example of my favorite approach:
Given the relative rarity of libertarians, both in the public eye and in general, most people’s judgment of libertarianism will be based on a very small sample – often a sample size of one. If the first libertarian someone meets is a smart, reasonable, decent person, they will come away with a positive impression and possibly a willingness to explore further. If the first libertarian someone meets is a wild-eyed lunatic, on the other hand, they could easily write off libertarianism as the ideology of wild-eyed lunatics.
This is why, when I talk to young libertarians about how to spread their ideas, I say they should think of themselves as ambassadors for the movement. That means, first and foremost, presenting themselves as fundamentally decent people that you would actually want to have a beer with; and second, being willing to admit the diversity of libertarian thought (“libertarians don’t all agree on this, but…”) before pushing their own peculiar views.