1) find as many people as you can to tell them of their experiences with nice pit bulls
2) introduce them to nice pit bulls
3) ask vets and groomers who work with them to describe how they can be

Stereotypes are hard to break sometimes. I happen to be a groomer and I have NEVER come across a nasty pit bull. I know someone with 3 and they may be rambunctious but never cause you to be afraid. My dad is one of those people that only believe the bad news that they read in the newspaper. Just because there are some bad ones (Made that way by humans) you cannot condemn them all. I have been bitten more by schnauzers and chihuauhuas than by any breed once thought to be nasty.