A very important factor in striking the ball solidly and consistently with your irons is getting the “bottom” of your swing in front of the ball (i.e., the lowest spot in the swing’s arc on the target side of the ball — see picture)
This promotes contacting the ball before the ground.
You can develop a feel for this by putting a tee in the ground about three inches in front of your ball, with the objective being to rip the tee out of the ground during your normal swing. In order to accomplish this, you’ll need to continue club head speed beyond impact, allowing you to reach the tee and the bottom of your swing with ease.
Once you can do this, you’ll hit your iron shots much more solidly and with more control.