I wouldn't say good course management is always laying up on Par 5's, but recognizing which ones to go for in two. If you have read "Every Stroke Counts" you get to read some polarizing statistics and one of them is that amateur golfers should always go for the green in two. However, this is provided there are no OB, water hazards, etc in play. It goes on to say that non pros are not good enough to stuff it within 10 feet with a wedge in their hands every single time, so you are better off hitting it as long and straight as you can. Closer to the hole, the better the odds of making par.
Things like punching out vs going for the gap between two trees is obviously course management. But things like club selection, assessing the lie, where to miss, how will the ball come out of wet vs dry sand, and when to be aggressive or defensive are also some things you should consider. Course management can be worked on anytime, and on every shot. Think your way through a course, and plan out how you are going to hit your next shot, will greatly improve your scores.