"Swing faster for more distance." This is a refrain that we've heard from many instructors; Hank Haney recently told Joe Namath (The Haney Project) to speed it up and swing "OUTSIDE" himself. He was pointing out to Namath that he was capable of far more club head speed than he was demonstrating. I've had my beginning swing speed measured at about 84 mph on average, and I believe that's on par with many golfers at my level of play. With my driver, I can hit it about 210 on average, which isn't really great.
Physics backs the notion of velocity adding much craved distance. For every extra mph, about 2 yards in distance is added. But how to add speed the right way?
We see players like Ernie Els swinging in apparently slow motion but with clubhead speeds well in excess of 120 mph. How the heck do guys like Els and Couples, with their languid, lazy looking rhythms, manage to hit the ball so far? These guys take 9-irons and hit them 150 yards. How do they swing slow and lazy but obviously still generate club head speed?
When I think of swinging fast, the first thing my subconscious brain tries to do is throw the club from the top really fast. And this causes mishits, OTT moves, slices, and no end of other errors, because as Namath said to Haney: "I'm trying to swing WITHIN myself." Haney was trying to relate to Namath that his swing was too slow where it counts--down in the impact area at the bottom.
In other words, a violent transition and adding speed too early will cause errors and the swing will ironically slow down before it gets to the ball. We need to start down SLOWLY and gradually add speed in the right place.
Shawn Clement had a beautiful swing analogy for speed. When pushing a child on a swing and satiating the child's desire to go higher and faster, the adult must ASSIST MOMENTUM where it makes sense--AT THE BOTTOM! The adult gives the child a gentle but firm extra shove at the bottom to increase the speed. When thought of this way, it's easy to see why many of us amateur golfers screw up the speed part and lose distance or accuracy or both. Applied the analogy above, we might kill the child with this way of thinking.
You can swing "within yourself" (with an Ernie Els-like rhythm) and still get the club head moving through impact 20 mph faster than you do now. You'll be more likely to keep some accuracy while adding distance. Start down slowly and gradually add speed at the bottom. This feels very subtle, gradual, and dynamic. Use counting rhythmic meters at a moderate tempo to help pace your swing. Just think of Clement's swing analogy and practice it that way. This also will give you two speeds to swing every club: your "normal" pace, where you get moderate distance and your "boosted" pace, where you get extra the distance.
You must also ensure that you're creating a wide swing arc going back and extending fully going through; really concentrate on straightening the right arm as the torso continues turning left. (Updated 1 Mar 15)
Simple: speed. Adding extra miles per hour to your swing is the only thing that's going to allow you to hit each of your irons farther. Most amateurs think of speed as something they generate from the top, but that's a recipe for almost every bad shot you can imagine. The secret is to maximize the fastest part of your swing, and that comes after you strike the ball.