Bruno Walter used the word knack to describe the art of rehearsing. Conductors have to find and develop their own knack; no two will go about it in the same way because of their different personalities and musical ideas. But most experienced conductors would agree on a number of basic principles to pass on to their younger colleagues:

The most important thing about a rehearsal is that it's not an end in itself. Everything a conductor does must aim at a good performance “on the night.” It takes experience to learn how to give your all yet to keep something in reserve. You have to be involved without performing and objective without being detached.

This balance is hard to strike because you obviously want to show your involvement in the music. The players need to see that you believe in a piece with every fiber of your being and are confident in your interpretation. If you can convey that, they'll feel inspired and really work with you. If you're not convinced, you'll never convince them.