Plenty of close calls have taught me the value of always knowing my exits and always leaving plenty of space between me and the car in front of me (driving instructors often teach 1 car length for every 10 mph: 70 mph = 7 car lengths).

Unfortunately a lot of these rules only work if other drivers on the road are also following them (around here, in the Boston area, you'll be lucky to have 2 car lengths of space in front of you no matter your speed), so I've learned that simply being aware at all times (no phone, no distracting conversations, and holy hell no text messaging or emails) is the best thing anyone can do for improving their safety while behind the wheel.