The biggest things I can think of are these.
1: Slow Down.
If the weather is bad, if it is an area with people, if it is on back roads with deer or if there is anything odd going on, slow down. It is much easier to stop and you have more time to react. (Trust me about deer because they can jump 20 feet out of the woods and land right in front of you, and there is nothing to wake you up quite like hitting a moose at night either).

2: Leave lots of space between you and the other cars. Even when you pull up behind a stopped car you should leave enough space that you can steer around it. When in traffic you want much more space than that in case the car in front decides to stop in a sudden fashion.

3: Keep your windows clean.
People argue over windex, ammonia or vinegar, but whatever you use is not as important as having clean windows is. Grimy windows are hard to see out of, especially when driving into the sun or when facing headlights at night. You should include making sure you have good windshield wipers and that the washer fluid is full.

4: Learn to use your mirrors and learn how to adjust them properly. You want to eliminate as many blind spots as possible.
Also you should adjust them so a set of headlights behind you don't reflect directly into your eyes. After a while the head motion to check your mirrors should be so automatic you forget that you are doing it but notice immediately if the mirrors are out of place.

5: Do your vehicle maintenance like a religious act of devotion.
Before starting the car all fluids should be checked along with a tire inspection. You should be checking that all your lights work at the same time. Most drivers don't check that often and some only check after the idiot lights come on. If you are not going to check every time you start a trip then at least do it each time you fill the gas tank.

6: Drive or don't drive, nothing in between
When you get behind the wheel you should have a clear idea of where you are going. Read the maps before you get in the car. If you need to check a map or make a call pull over some place and stop to do it.
You need no extra distractions when driving.

7: Don't drive tired. I have seen 8 accidents caused by people falling asleep behind the wheel, 3 of them resulted in deaths. If you are tired pull over and have a rest, even take a nap if you must.

Finally: Did I mention slowing down?