I second this. I rowed semi-competitively for years in my teens and early twenties, and thought I had good form. I didn't learn until after herniating a disc that it's important to do most of the drive through the heels rather than the ball of the foot. Most people learn not to overreach at the catch, which is part of it, but you also have to focus on not just getting the heels down, but actually driving through them. (Much like squats, another thing I didn't learn to do properly (with weight on the heels) until after that injury.)

Of course there's a bunch else to it - keeping the back straight and strong, etc. - this was just the thing that happened to be missing from my training, so might be for others as well.