In reply to 80sFast :
I like to work on smoothness with the brakes, getting on and off. I try to be able to get quickly from gas to brakes, but still hit the pedal just enough to take the slack out of the system, so there's no real braking, just getting all the slack out of the pedal, lines, calipers... Then try to get smoothly and quickly (not too quickly, remember that the fronts will develop more grip as more of the car's weight is transferred) to the amount of deceleration I want for the slowing or stopping I'm going to do (paying attention to whether I get it right and have to make adjustments). Then I try to trail off smoothly and slowly so that if I'm stopping, there's little to no "pop" at the end where the front end comes back up, because I've been bleeding off the pressure right up to the stop.
The benefits of not wasting time between gas and brake are obvious. But it's important not to jab at them as you transition, so you need to be smooth when you get there. Fine control and modulation of the brakes is important, and being able to taper them off smoothly and with control is... I was going to say important to trail braking, but I also think it just helps with a solid command of the controls.
Also, pay attention to how the vehicle reacts to everything you do, however subtle. Note that if you're going around a bend at 45mph and you ease up slightly on the gas, the line will tighten. If you speed up slightly, gently, the line will widen. Pay attention to how you probably automatically adjust the steering angle when you do these things. Pay attention to the fact that you're doing it. Pay attention to how if you accelerate a little more firmly around a tighter bend, you'll also need more steering input, but before you've gained more real speed, you'll need more steering angle because you've taken weight off the front tires. And the same applies for releasing the gas pedal or doing some braking; you'll need to ease up on the steering. Summing this rambling paragraph up, pay attention to how weight transfer affects what the tires are doing, how throttle affects weight transfer, and how speed affects inputs.
I spend a lot of my attention in normal driving trying to be really, really smooth. I want my passengers to not notice when I shift. I don't want to make mid-corner corrections with the steering unless there's a reason to change trajectory.
Also, focus on looking ahead. I probably should've written this as item one, even though it's already been mentioned. That's been one of the biggest struggles and the biggest payoffs in autocross, track days, mountain biking, karts... Get your eyes up. It reduces the sensation of speed, lets you decide where you want to go so you're not reacting late, and tells you about trouble sooner.
Anyhow, that's stuff I do, but I'm no authority. I feel like it's stuff that helps me, and entertains me too. There's plenty more, but I suspect that the reading list will help, too. Most of my stuff starte with reading Frere and others many years ago. I think Jackie Stewart wrote some stuff that also had an impact on me in terms of smoothness. And I can't remember whether it was Stewart, Mario Andretti, or something else who said something that stuck with me about how saving a big moment might make you feel competent, but you should actually set your sights higher and in that case be cross with yourself for having had a big moment in the first place, not pleased for saving it.