Open air preaching, whether on campus, on a street corner, or at a special event, is simply a preacher or group of preachers finding a crowd (or drawing one) and preaching to it. You must pick a well trafficked place, lift up your voice, and rely on the Holy Spirit to work with you in drawing crowds. A preach can be as brief as a "drive-by" one-liner from a passing vehicle, or can last several hours and typically includes a few loud mouthed hecklers who attempt to distract and/or derail the preacher. However, a very obnoxious heckler can be a gift from Yah because, if used correctly, the heckler can help you create conflict and draw an even larger crowd. The very person who is trying to discredit or anger you, unwittingly winds up drawing more people to hear your message.
When preaching, there are a few simple rules that would be good to keep in mind. Make sure to pick a public place and not private property. Some private universities will allow you to preach if you had received prior permission or obtained a permit. Most private places will not allow you to preach on their property. If you are preaching at an event or a place where there are an unusual amount of police, it might be good to talk with one of them and let them know what you are planning to do. Working with the police at events where crowds can get hostile is essential to staying out of jail. And remember, if a crowd does become so hostile that they are no longer listening, it is best to leave and try someplace else. You must listen to the Ruach Ha'Kadosh, of course. Stephen had a violent crowd, but chose to stay and he was, of course, killed as a result. Often times, rather than getting killed, injured, or thrown in jail, it is best to simply wipe the dust from your feet.
It is essential for a street preacher to listen to the Ruach Ha'Kadosh whenever you go street preaching. The Ruach Ha'Kadosh will be your most faithful helper in avoiding the perils and pitfalls that can accompany open air preaching. The most important thing to do is to obey the Scriptures, and open your mouth to preach!