|The Deep Stuff!|
First, your angle of attack is very important. If you have a steep angle of attack, you will not catch too much grass before you hit the ball. If your attack is shallow, your club will have to fight through the deep grass and you will lose power and also some accuracy. The easiest way to accomplish a steep attack is to set up to the ball with an open stance and a slightly open club face. Once you set up in this way, remember to swing along your set up lines and not down the target line. This will give you an out to in swing path. This swing path might take away some of your power, but it will be better to give up a little distance than to fight through the rough. You might be tempted to take more club to get more distance, but remember the adage, "loft is your friend in the rough"! There a lot of reasons for this adage. First, lofted clubs are shorter and will swing on a steeper plane by design. Second, your goal is to get the ball up and out, which is the picture you should have in mind when you step up to a shot in the deep rough. Low lofted clubs will often drive the ball directly into the rough in front of the ball and take away distance, direction and the opportunity to play your next shot from the short stuff.
Next, you should think about your swing differently when in the rough. When hitting from the tee or the fairway, you will have smooth acceleration from the top through to the finish. The club will be released at the bottom of your swing with extension through to your finish. In the rough, you want to take a firmer grip on the club and accelerate to the ball, but not necessarily release through the shot or try to make a full finish. This is because you need more energy going down instead of through as in a regular swing. When hitting long shots from the rough, your finish will be less than full, with the handle leading the club head through the shot a bit more than normal. Leading with your handle will give you strength as you swing down and through the ball.
When hitting shorter shots from the rough, I have seen some of the greats take a firm grip, but still manage to release the club with very little through swing. The openness of your set up and short club choice will create the downward motion needed to get the ball out and by allowing the club head to release a bit, you can still get some height on the shot. Even though you are releasing the club, remember to keep the club moving down through impact.
Rory McIlroy in deep greenside rough Check out this link to Rory in a practice round practicing from the deep rough. You can clearly see the "down" motion of the club and also the release he makes to get height on the shot.
Finally, remember that your club is doing the work when you are in the rough. If you try to help the club by scooping or getting behind the ball in the downswing, you will release the club too soon and catch too much grass. It is crucial to keep your weight moving to or even anchored on the front foot if you want your swing to have a lot of "down" in it. Most of the work in the rough happens in the downswing, not in your finish. By not making a full finish, it will be easier to keep your weight on the front foot. If your focus is on making a full swing from the rough, you will inevitably fight through the rough and end up watching your shot from the back foot. By the way, it will not be a good shot.
These three strategies should help you get the ball out of deep rough more easily. They are to set up a bit open with both your stance and club, focus the swing's energy down instead of through and stay anchored on your front foot as you make the swing. The other little things I mentioned such as "loft is your friend" are tough to take when it seems taking more club will be the key to getting you to the green, but in the long run they will save you strokes. You can usually practice from the rough if you go to the far side of any range. A little practice will teach you a lot! Good luck next time you are in the thick stuff!