Evaluate the worth of your video. Ask yourself objectively if it's something the TV news stations would want to buy.
Act in a timely manner. Video loses its timeliness very quickly, and TV news is all about what is happening right now, not what happened a week ago.
Call the stations. Ask to speak to the assignment desk. These are the people who decide what gets covered by whom. They book live shots and coordinate crews.
Explain what video you have, how much there is and why they'd want it.
Tell the station that you're talking to the other stations, too. This may prompt them to scoop up the video to beat the competition.
Set a price. Unless you've sold video before and know what the market pays for it, negotiate the price with the station management.
Ask the station to courtesy the video. This means the anchors have to say where the video came from. The producers can also put a courtesy graphic on the bottom of the screen. If you're an amateur, this isn't necessary. But, if you hope to make a career as a stringer, this will help get your name out there.