I spend more time than I like in rush hour traffic on the interstate. I have always tried to position myself toward the center of the lane in order to give the cagers every opportunity to see me in their drivers side mirror. I also never ride in the blind spot off the rear wheel. I am either completely behind, or I get up next to the driver's door so they HAVE to know I'm there.
I was talking with a friend of mine once, who is a certified MSF instructor. He said my technique was wrong, that I should stay as close to the car in front of me and as far from the traffic in the other lane as I could. He said this would give me more time in case someone tried to come into my lane. I told him my intention was to make certain they knew I was there so they would not come into my lane. We agreed to disagree.