A lot of what determines whether you hit a good or bad shot happens at address. The simplest thing is ball position. If you get the ball in the right spot, good things tend to fall into place. Get it in the wrong spot, and things fall apart.
I like keeping the ball in the same position for all clubs on standard full shots. Start with the driver: Play it in line with your shirt logo, and drop your right foot away from the target in a wide stance (below, left). This sets up an upward strike.
For a middle iron, don't move your right foot out as wide and keep the ball in the same place relative to your front foot. This narrower stance puts you more on top of the ball so you can hit down on it (middle).
When you get to the wedges, the stance is the narrowest and you even lean a bit toward the target at address (right). From there, you can really hit down and rip a divot after impact.
In short, it's about how wide the right foot goes. That sets the relationship of the body to the ball—but the ball doesn't move.
People tend to get fixated on the ball and try to lift it at impact. That leads to thin contact and even topped shots. Here's a drill to get you hitting down and through the shot. On the range, tee up your iron shots like you do on a par 3. Then focus on knocking the tee out of the ground. You'll hit down more at impact and start really compressing the ball.