Long Irons - It's Just a Number
Don't think about how hard it is to hit a 3 or 4 iron, simply concentrate on making the same swing you would with any iron, especially the short irons. Just pretend that you have a seven iron in your hand instead of a three iron. Make your normal swing and don't think about anything else. After all it's just a number printed on the bottom of the clubhead that is causing all the worry. If you didn't know what club you were hitting you probably wouldn't worry about it. You would just try to swing like you normally do.
So next time you are faced with a long iron shot just concentrate on making the same swing that you always do. Even pretend that you're hitting a short iron. I bet you'll strike the ball better and end up with more consistent results.