These exercises will help you develop your vision while driving.
Before checking your mirrors to see if there is a car to your side or behind you, mentally ask yourself if you think this is the case.
Soon you will find that you can drive for extended periods of time without actively checking your mirrors, and yet have a pretty accurate idea of which lanes have cars in them.
Many street drivers have attention windows that extend as far forward as the rear bumper of the car they are following. For track driving this will not do.
A good number of cars to watch is 3 in your lane in front of you plus 1-2 cars in lanes adjacent to you. Obviously, more is better.
If you are driving a manual transmission car on a highway, you should have enough engine braking to modulate your speed without using brakes. The key is being aware of what the cars further in front of you are doing and accounting for that appropriately.
You are doing well if you start to decelerate for congestion/traffic before the brake lights turn on on the car immediately in front of you.
Watching Vehicles You Cannot See
How do you look 3 cars ahead if the car immediately in front of you is a pickup truck or an SUV and you cannot see through it?
Look around it!
If you are driving in daylight, chances are vehicles cast shadows. Often you can see the shadow of the vehicles ahead of you even when you cannot see the vehicles themselves.
When the road curves you can see many cars ahead of yourself. Make note not only of the cars, but also spacing between the cars. Identify cars that are following with long distances and those that are following with short distances. Which ones should you be paying attention to?
If you are driving at night, you can see reflections of tail lights on the pavement and other vehicles and you can also notice the brightness difference between tail lights and brake lights. This way you can tell whether a car is braking without having a line of sight to that car's brake lights.