You’ve probably been told by your driver's ed teacher to NOT left-foot brake. So most drivers have not developed this skill, even though it is hugely important for performance driving. It's very common for people who are new to left-foot braking to flinch and press the brake and the throttle at the same time in a panic situation or use the clutch instead of the brakes. A good way to start using left-foot braking is to keep a bit of gas on so the car continues moving and put your left heel on the floor and use your ankle to apply brake pressure. Even if you're driving down the highway, you can still experiment with different brake pressures to feel how the car reacts to them and get your left ankle trained. At first you may be jerky, but smoothness will come as you get the hang of it.
Left-foot braking can get tricky when you need to shift. If you are entering a corner in third gear and exiting in third gear, left-foot braking is an excellent technique to apply. When you need to shift, move your left foot over to the clutch to shift and then bring it right back over to the brake pedal. A lot of drivers think if you are left-foot braking you can’t shift but that's not the case. Use your left foot on the brake to get the car slowed down beforehand and then shift whenever it is necessary to do so. It is also acceptable to right-foot brake and heel-toe-shift and then get your left foot back over to the brake pedal. Even if you're not driving fast, it's good practice to get your left foot always covering the brake pedal in hazardous or performance driving situations because it significantly decreases your reaction times. If an animal runs out or someone pulls in front of you at the last second, having that left foot right there means you can get to that brake pedal a lot sooner. Another option for shifting is to shift without the clutch. If you shift without the clutch, your left foot can only be used for applying the brakes.
It's really important to practice left-foot braking in your daily driver before you need to use this technique in a motorsports environment. If you are planning on coming to Team O’Neil attend the Rally School, coming in with some experience with left-foot braking and some smoothness will certainly give you a leg up. Give it a try out and be safe out there!