Get a Rolodex and never lose a phone number. Ask people how you can reach them after hours.
Get a calendar and never miss an appointment, or call if you have to miss something.
Return all phone calls, even if it's late and no one will be there to answer.
Get a file cabinet and use it.
Remember everyone's name and be nice to everyone, especially the less important people. I got one of my best stories from a janitor.
Thank people who helped you on a story after the story has run. Consider writing some people thank you notes.
Try to make your first several stories positive. If you start out with negative stories, you'll burn a lot of sources right from the get go. Once people know you, they won't freak when you do negative stories and they'll often leak you good information.
People hate it if you don't have any opinions--you may come off as fake. But you don't want to make them think you're biased. So have opinions about things off your beat, like the new Spiderman movie or the best restaurant in town.
A good book for reporters: The Straight Scoop: An Expert Guide to Great Community Journalism by Hartford Courant. (It's out of print and hard to find but worth ordering).