I can’t provide tips, I can only tell you what I do/have done. I’m not saying “do this". Just n=1. I have never tried to improve my sprint as other than being fun, it serves a limited purpose for me (primarily an XC racer, and there are limits to traction**).
I’m spinning, fast. How fast? No idea. But it’s up there. I like longer cranks for my height, so maybe I would hit bigger numbers with shorter cranks, but I’m not interested.
I’m NOT lifting the back of the pedal. If I do, my cleats will pop out on my road bike. But I’m certainly not weighing my pedal down on the back side, and that does matter. I think it is more that I’m concentrating on being smooth, and applying maximum effort on that short period of time when you can.
It’s a whole body experience. Core, arms, legs, everything is working in unison for me to hit those numbers.
I’m sure lifting weights would improve the numbers, but I haven’t done a dedicated gym routine in well over a decade. Problem is I like riding my bike too much, so I don’t want to skip riding to go to the gym*.
I also run a lot, no idea if that makes any difference.
I absolutely get walked on by the local fast crit guys, so that 1000+ watt sprint isn’t doing me any good. It’s all about tactics. Since I don’t road/crit race, I only do local practice races where I am there to destroy myself for the workout while they are out there to train for races. So when the finish line appears, they just walk right on by me. Getting that power is cool and all, but it won’t do you any good if your tactics suck (my tactics suck).
*I go to the climbing gym for upper body work, otherwise my upper body gets too weak and I get injured mountain biking.
**MAYBE having to “sprint” up hard obstacles (more peak torque than peak power) is related, don’t know.