On your marks. Set. Go! The sprint start is all about overcoming inertia and gaining momentum. It's propulsion exemplified. The start sets up our acceleration. There are 4 main ways we can perform starts. There is a 4-point, 3-point, 2-point, and rolling technique which we'll examine.
The 4-point start uses four points of contact with the ground...thus the name. This is also known as a block start becuse of the use of starting blocks. The blocks allow you to get your feet oriented so that you can apply more horizontal force and project yourself forward more than just upward. If you have the opportunity to access starting blocks, and practice with them, they are amazing. However, blocks aren't always available for us Lifetime Athletes. While you can do a 4-point start without blocks, I usually don't recommend it. Doing so places excessive stress on your ankles and achilles tendons and puts you in an awkward position. A blockless 4-point start is often slower than a good 3-point start. Try blocks if you can, but don't worry about them if you can't.
The 3-point start is our gold standard when we are serious about takeoff from a static position. Stand in a front-to-back staggered position, with the strong foot forward. Experiment with how far back you place the rear foot. You don't want it too stretched out because this causes you to lose propulsive power. I like the toes of my back foot to be just an inch or two behind the heel of my front foot (feet shoulder width apart), but everyone's linkages and levers are different so definitely test this out for yourself. If your right foot is forward, touch the fingers of your left hand down just behind the line (if there is one) and the right arm hanging freely. At the "Set" command, cock the right arm back, raise the hips slightly, and lean forward so you feel more weight on your front foot. At the gun, or "Go," push hard and aggressively reverse the limbs, coming out at about a 45 degree angle and almost falling on your face. The first three steps are big pushes, but the first is longer/stronger than the second and the third is less so than the second. Gradually rise and work your way into upright form. This can require anywhere from 10-30 yards/meters depending on the athlete's ability level, and the distance of the event (e.g. 40 yards versus 100 meters).
A 2-point start is often called a "crouch" start and you'll see this in most track events 800 meters and up. Even though this is the static start of middle and long-distance racing, it's actually used quite often in sprint training. That's especially true when running longer reps in practice. Simply stagger your stance and lean forward just shy of the point where you start to fall. Then release yourself and take off.
The rolling start is a great way to get going without as much tissue stress. This can be a casual couple of skips or steps and then letting cadence build. Or it can be more of an official "run-up" for a flying start when hitting a cone zone for max velocity.
At our level, the main thing to work on with starts is getting comfortable with the positions so we can set up effective acceleration. The rookie mistake is to just stand up straight and start running hard, which is not as effective as driving out and making that force application from horizontal to vertical more gradual.
Starts use different movement patterns than upright running. "Quadruple extension" of the ankle, knee, hip, and trunk occurs powerfully during starts and this is most evident from the lower positions in the 4-point and 3-point. This requires strong glutes, quads, and back extensors.
Starts are a skill and they are an important, fun, and challenging aspect of athleticism that we need to practice. Getting off on the right (or correct for you) foot makes all the difference.