One of the most common problems I see with many weekend players is a too long backswing. I say problem because it contributes to so many mis-hits and errant shots. Most of my students don't realize how far they are taking the club back until they see it on video.
So how long should your backswing be? It depends on a number of factors. Your build and body type have considerable influence. Are you stocky and thick chested or tall and slim? The slimmer person naturally will have a longer swing because he has less body mass for his arms to swing around. Are you young and supple or older with less flexibility? These things are determined based on your body type and flexibility. Besides stretching there isn't a whole lot else you can do about it.
What you can do is determine the correct backswing length for you. Here is the drill I use with my students and it isn't difficult to do. Simply take your adddress position with a middle iron. Then while maintaining your posture hinge your wrists where your thumbs and forearms join moving the shaft and clubhead upward toward your head. Then turn your shoulders to the right while maintaining your spine angle.
Your arms and the clubhead will now be at their correct backswing length. Do this facing a full length mirror and you'll be surprised that in almost all cases the shaft will be well short of parallel.
Practice this until the new position begins to feel more comfortable, then hit some balls starting with short irons. You'll soon be hitting more solid and straighter shots with no loss of distance.