First scout the market. Call your local television stations. Find out from whom they obtain their stringer footage. In some markets, when you have a news worthy story, you'll have to approach the stations directly. In bigger markets, you'll be dropping your tape off at an agency that will supply the footage to the stations via a feed.
Get yourself a quality ENG electronic news gathering package. For many years, Betacam SP was the standard. In fact you can't really go wrong shooting with a Sony Betacam 400A, still one of my favorite cameras. Every television station and distributor in the US has a Betacam deck. However it is possible today to get by with a far less expensive DV camera. Be sure to get one with at least 3 CCD's, the bigger the chip, the better. The detail of DV is comparable to Betacam although the color isn't as good. Although I've shot a lot with mini-DV, I'm not happy with the fact that many DV cameras have to be held by both hands in front of the shooter. As a stringer you'll be doing a lot of hand held shooting, so choose a camera that can mount on your shoulder for stability. You want a long lens, at least an 18x, or one with an extender so you can get good sized images if you're not allowed to get close. Make sure that your camera can accept external microphone inputs. You'll need a good quality mic to conduct interviews.
Get a non-descript vehicle. When I shoot news, I'm typically in a van with easy access to my gear through the sliding door. You don't want to show up on a crime scene with a flashy car.
Since you are strictly working on spec as a freelance shooter, you have to know what sells. As you're listening to your scanner, here are the stories that are most marketable: Disasters likes major fires, earthquakes or tornadoes, acts of terrorism, hate crimes, celebrities behaving badly, shootings, murders, violence against family members especially children, police shootings or brutality, rescues of pets or kids, or fatal car accidents. Don't bother with routine medical emergencies, minor traffic accidents, natural deaths, overdoses or suicides unless they involve celebrities. As you see you've got to have the fortitude to cover people at their worst.
Overcome what ever natural reticence you have to get interviews with witnesses. Remember the basics, asking Who, What, When, Where, Why and How. Get your interview subjects to spell their names on camera and give permission to appear. Even if you've never written more than an email, get used to the fact that to sell your video, you'll need a hook that will interest the news directors or producers at your local stations. A story titled "Joy Riding Drunk Teens Cause Death of Family of Four" will grab somebody's attention more than "Four in fatal accident."
Look at my other postings on how to tell a good TV news story and get clear audio. You need to be able to tell a story with your camera. Whether or not you ultimately make a dime for your efforts depends on how good your video is.
Finally, make sure that you treat first responders right. You plan to make this a career so don't alienate them. They have a job to do and will respect your attempt to do yours if you're friendly but deferential. If by any chance you arrive at a crime scene before the police do, proceed with caution. A lot of people aren't too keen about being exposed on camera. Be sure to leave the scene with your expensive gear, before the cops depart.