Ironically, he wants you to hit more balls from the rough.
Here's the deal: Zander says most players don't stabilize their clubs enough at impact. It's a balancing act, after all -- you want to remain relaxed enough to let the club swing easily, yet not so relaxed that the club can be knocked off-line or stopped by the ground.
His solution is to practice hitting half-shots from the rough, since that will make you automatically firm up your grip at impact:
Here’s a tip to help you get the most out of hitting balls from rough. Zander says that you need to get that feeling of connectedness between your arms and your torso to hit solid shots. To practice that, he says, “At address, feel pressure in both armpits, the biceps pressed against the chest. As a drill, tuck the sleeves of your shirt under your arms and practice making half swings, keeping that pinch.”Zander says this will give you immediate feedback if you're not making a firm, decisive swing at the ball. Then, all you do is try to recreate the feeling when you make a full swing. Makes sense to me!
The article is short but the advice is easy to use. Best of all, you can use this drill even during a round if you feel the need to refresh your memory about how your swing should feel. That kind of drill is a win-win situation for any player!