Well, same as any other fear, you have 1) face it and 2) do that bit by bit. Ride one block on the street. Did you survive? Cool; your fear is now ever so slightly diminished. The next day, two blocks. And so on.

It does help if you are confident in your ability to ride in a straight line and to brake on a dime (aka using mostly the front brake). And, same as passing a truck on the highway in a car, it's generally not a good idea to hang out in a car's blind spot. As for cars that are scared to pass you, yea, that's really obnoxious. But as mentioned elsewhere in this thread, the vast majority of bike-car accidents don't happen on the straight-aways; they mostly happen in intersections.