From Kevin Craggs:
How to stop fat strikes: A simple way to quickly clean up your strikes is to focus on firing the left knee back on the way down creating a firm left side at impact which keeps the upper half of the body tall preventing the club from hitting the ground first.
• Avoid breaking the wrists quickly and lifting the club up too steeply with your arms in the backswing
• Fire the left leg back on the way down whilst maintaining your height through impact
• Check your ball position is not too far back in your stance
• Apply a bit more grip pressure too your left hand and maintain the pressure throughout the swing
• Make sure you don’t release the club too early with your wrists in the downswing maintain the angle as long as you can

How to prevent thin strikes: The thin often appears when a player is under pressure the grip becomes tighter the arms become stiffer and the body movement is restricted. The easiest way to ensure a positive strike on the ball avoiding a thin is to focus on gripping the club softer allowing your wrists to hinge on the way back and on the way through.
• Keep the grip pressure in both hands very light
• Concentrate on keeping your forearms apart at address don’t squeeze them tightly together
• Make sure your weight is not too much on your heals during the downswing
• Focus on maintaining your spine angle during the backswing and avoid any straightening.
• Allow your wrists to hinge back and forth throughout the swing

Marc Warren's three quarter iron shot

The three-quarter shot iron is an excellent shot for any player to have in the bag. It gives you an option when you're between clubs, it penetrates into the wind, but above all it helps control distance. Club golfers often go about the shot wrongly, usually making a shorter backswing then throwing their hands at the ball. Instead, I'll show you how letting your right elbow fold close to your side on the way back puts your body in charge - resulting in a solid, repeatable action that gives you control.

Set-Up - Pre-set a Short Swing
I'll narrow my stance by perhaps an inch, and go a quarter of the way down the grip. Both changes promote a more compact action. I'll probably lose about 10-15 yards on this three-quarter shot, and about half of that comes from these set-up changes. Ball position stays just forward of centre.

Backswing - Right Elbow Folds
My focus is on my right arm controlling the length and pace of swing through folding the elbow. If it stays close to my right side on the way back, I'm sure to make a shorter, tighter swing; if my right arm were to stay straighter and wider, it would create a much longer swing. From here I simply turn my body to the top, taking hangs and arms out of the action.

Downswing - Body Dominates
Keeping my right elbow tucked in coordinates my arms and body, and that helps me take the hands out of the hit on the way down. One final thought - aim for your throughswing length to mirror the three-quarter backswing. This shot is about control, and a shorter throughswing is a good way to calm your action.