I'll give a couple examples of my bad technique. First of all, one sure indication was that I used to get multiple blisters on my hands. This is not something that should be a problem with proper grip and strokes, and it has not been a problem since I corrected it. But remember I was a teenager with limited resources, and I knew very little about anything. So at the time, I was under the misapprehension that I just needed to practice more and develop calluses so that I would not blister any more. This didn't work, of course. Also, my left hand was ridiculously weak, so I way over compensated with my right hand, making it work more than I should have.
As for the pedals, let me start by quoting part of mikel's post above:
That is more than my teacher ever spoke on the subject. Again, me being a clueless kid, I looked at the kick pedal and thought, "Ok, my heel must go on the heel plate and my foot should line up perfectly with the footboard." I didn't know about heel-up, or whether I could slide my foot back or forward on the footboard. There were other factors too, like how my foot was aligned (or misaligned) with my leg, the height of my seat, the distance between the seat and the pedal, etc. What really never occurred to me in heel-down playing was thinking about the upstroke as well, or lifting the front of foot as well as pushing it down. All of my energy was spent pressing downward. This constant pressing down hard into the pedal would cause my foot to slide forward against the toe-stop, and as I kept pushing, my heel would actually start sliding outward. Put it all together and it did not work well, so I would just put more and more muscle into it until I achieved what I wanted, or close to it. Once I started analyzing things carefully, I realized this caused tension from the tips of my toes all the way through my leg and into my lower back. And as I mentioned before, I was burying the beater all the time but also getting unintended rebounds that made my kick work sound sloppy. I wasn't even aware of it until the first time I entered a recording studio and the sound was isolated. My kick technique was a mess, basically. I think a lot of this could have been avoided with some simple instruction like this from the beginning:
https://www.youtube.com/watch?v=7LQoVrPxkNk
Between my legs and hands, I must have looked like one big ball of tension when I played, which I think a good teacher would spot and correct immediately.