Doing a head check when changing lanes should be law. I don't care how well you think you can see, or that you think your car doesn't have a blind spot. It might not seem that way sitting in your driveway, but you can't see everything in your mirrors going 100 on the freeway.
I can't count the amount of times I've almost been side swiped because of this. Luckily my dad is a professional driver, so I've been taught to drive very defensively.
Oh, and if you're going to do less than 95 on the freeway, get into the left lane.
Oh, and if lanes are merging, don't want until the last minute. It slows traffic so badly. Ie - just before the bridge on Chander Hwy in Alphington around 5:30pm - nightmare!
There's so many more, I loathe bad driving.