Practicing Golf and Playing Golf are completely different animals, and should be approached with totally different mindsets. Trying to mimic a practice session during a round is detrimental to good play, and trying to mimic a round during a practice session will hinder the learning process.
Practicing:
The driving range and practice putting green are the places to tinker with your swing and make adjustments. Feel free to analyze different components of the swing and try new ways of doing things to test their effectiveness. Practice with purpose, and think about how one action changes another action.
I practice two different ways. One way is to try and shape shots different directions (hook, slice, fade, draw, knockdown, punch, lofted shots, etc.), even hitting extreme hooks and slices just to get the feel for spinning a ball off the clubface to get it to curve a particular direction. Practicing in this manner teaches the golfer how to build an arsenal of shots that will come in handy in many situations on the course. Simply attempting to hit straight shot after straight shot will not only be quite defeating (as no ball really ever flies completely straight), but there is very little to learn from this technique. This method of attempting to shape shots and be creative with practice sessions is the most common for me.
The other way to practice at the range is a bit more similar to playing, but not quite the same. I'll take a bucket and just hit balls without thinking of shaping it one way or the other, or in other words, just swinging the club as naturally as possible. I will be very aware, however, of what the ball is doing in the air. I'll make mental notes on how many shots are drawing, how many are fading, how many I'm getting thin or fat, etc. This teaches me a great deal about my natural tendencies so that when I get to the course I have more of an idea about what my ball is going to do in the air.
Playing:
When you get out to the course, all swing thoughts must be eliminated, all analysis and adjustments put out of the mind, and all trust put in the natural golf swing. Trying to tinker with a golf swing during a round is a recipe for disaster, as this greatly decreases the confidence level of the golfer and thereby decreases the likelihood of a good shot.
If you must have a swing thought, have it be something like 'smooth tempo', or 'slow down'. The golfer must focus on staying relaxed and in the present moment. Visualize the shot you want to hit, based upon the tendencies you've noticed on the driving range or prior shots during rounds, and focus on the process and not the result.
