Keep the Takeaway Low
During long-iron practice, focus on taking the clubhead away slow, low and under control. I actually like to scrape the ground a bit and see a little grass fly. Similarly, as I come through the ball I try to take a long, shallow divot after impact, removing the blades of grass and exposing the roots. The longer the clubhead stays low and moves straight down the path through impact, the better your shots will be.