Rukee's experience with a 4-speed car hits all the significant points.
The challenge is keeping the tires right on the edge of breaking loose without actually spinning. It's a property of physics that it takes less force to keep
a tire spinning than it does to start
it spinning, so the ability to ride that edge will net you the best launches and best e.t.'s.
Once you learn how to do that, the second piece of the puzzle is tuning your reaction time. You want the car to be moving such that the second staging beam "reconnects" the exact instant that the green light comes on.
(There are two beams, pre-stage and stage. As you roll forward, the tire breaks the pre-stage beam first and turns on the top bulb of the tree. As you keep rolling forward, the tire breaks the stage beam and lights the next bulb. Depending on how large your front tires are, you've got "some distance" you can roll and still keep both bulbs lit. "Deep staging" is when you roll forward far enough that the pre-stage beam turns back off, but the stage bulb stays lit. If you allow the stage bulb to turn off before
the tree goes green, that's a red light and you lose. If you take a nap and let a bunch of time go by before launching the car, you can run a perfect e.t. and still get smoked.)
You have to learn how to be consistent - picking a point in the tree count-down where you launch the car such that by the time the engine has responded, taken all the slack out of the drive train, started the car moving, and the car has moved far enough to turn off the stage bulb.... all that has happened such that the bulb goes out the instant
the tree goes green. When you see your reaction time printed on your time slip, that's how much time passed between the green light and the stage bulb turning off (because your front tires moved out of the beam).
You want that to be a very small number - like .040 or less - and learning how to do that every single time requires a car that's consistent and a driver who knows exactly how "far" to roll into the beams and how to begin the launch at exactly the right time in the countdown. It's not easy, especially with a gallon of adrenaline dumped into your system from the excitement.
One approach is to always launch your car at exactly the same time. (Like the instant you see the last yellow turn on) and then "tune" your staging depth to adjust your reaction time. Stage "shallower" (don't roll in as far) if you're going red, stage "deeper" (roll in farther) if your reaction times are too long.
Depending on your car and your own physiological reaction times, you might have to adjust your 'starting point' to go some time on the middle yellow (when you see it start to go out, etc.) or later on the last yellow if you and the car are both extremely quick.
How important is it? Very. A difference of .01 at the tree can translate to a margin of .1 at the finish line.
It's why some racers invest in expensive electronic delay boxes and transmission brakes. With a delay box/trans brake car, you set a time into the box and then you always "leave" on the first yellow (because humans are more consistent that way). The delay box will then continue to hold the trans brake until the set time has passed, then release the trans brake and allow the car to launch.
There's more to it than meets the eye, but it's also an opportunity to have a lot of fun while you're learning, practicing, and improving.