Personal experience, the experts probably disagree with me, but: lock your doors and close your windows so they can't be yanked open, leave a bit of room in front of your car so you have someplace to go, be willing to run a light if it starts looking dicey. Most important is situational awareness, though. If you're rushing and not paying attention somebody else might be.
All of the attempts I'm personally aware of have been in traffic, but there was a group of kids (12-14 maybe, not just what the news calls "children" which seems to be anyone under 25) jacking cars at the Arsenal Mall in Watertown a couple of decades ago, and the MO was to go after shoppers with their hands full getting into cars.