The task of hitting the ball out of the thick rough should be taken seriously and not be underestimated. The odds of making a disastrous missed swing are significant, and just one hit on what seemed like a relatively easy hole can end up killing your otherwise great score for the day.
The most important thing to realize is that you will most likely lose twenty to thirty yards distance and the accuracy of your shot will widen to a cone of error spanning a large chunk of property where you would prefer not to be.
Also realize that if the grass is growing in the direction of the hole and you just happen to hit the ball perfectly clean, it could even fly out of the tall grass like a rocket ship targeting that body of water way over the green.
I try to minimize error by hitting down onto the ball and thereby avoiding chopping through too much grass. Swing like you need to punch it low through the trees. By mentally preparing yourself for the thick greenness obstructing your swing, make a more powerful follow through without forcing your normal swing too much.
Do it right and you can get a respectable bogie, maybe even getting lucky with a following chip and one putt.
Do it wrong, and accept the resulting punishment of a triple bogie because you topped the ball to the right even deeper into the tall grass or hacked it left into the water.
I guess the really hardest part is to keep calm. Realize your limitations even when you are having a stellar round and start thinking you have acquired supernatural golfing powers and can do anything.
In order to illustrate these concepts better, here follows a true story. These are my actual thoughts:
"Alright, so if I hit it just right and chop through with an open club face the ball will fly through that small opening between the trees, fade just enough to the right and possibly even roll up to the front of the green for a possible birdie putt..."
Then it all happens before I have time to realize it. The next three shots occur in rapid sequence, no thinking involved. Oops, topped the ball. Next shot hits the tree on the right and drops straight down. Third rescue attempt and I shank it into the other fairway. And so on and so on.
On the eighteenth hole, a stellar round is blasted into nothingness by my extreme foolishness and utter disregard of reality. Better luck next time.