Two things:

1. Always cast the best people you reasonably can.  I've sometimes had to make a choice between a phenomenal actor who was busy during the rehearsal period (e.g., opening another show), versus an actor who had no conflicts at all, but really couldn't act.  You will "waste" the same amount of rehearsal time whomever you choose, so you might as well go with the better actor.  If you go with the great actor, scheduling rehearsals where he can come may be a challenge, but you accomplish much more per rehearsal than you would with the lousy actor.

2. Always have a "vision."  This word sometimes scares newbie directors- they think having ideas for how they want a show to be will limit the creativity of the actors.  Not at all.  Good actors will take your vision and expand upon it.  And your vision will likely evolve during rehearsals.  Still, a vision is absolutely essential for a great show.

This is a great topic.

1. Everyone learns differently. For some actors, all you have to do is ever-so-slightly suggest a direction, and they get it and off they go to do great things. With others, you may need to get up there and walk with them for a bit. Accept the differences cheerfully, and do what is needed to ensure each actor succeeds.

2. Get up onstage and act once in a while so you remember how terrifying it can be up there and how vulnerable actors -- even good ones -- can feel without your help.

3. Don't try to be popular. Do what is needed to deliver the best product you can, even if that means going back through a scene when you think the actors will hate you for it. Inside, they know they need the work, and they will be grateful.

4. Praise, praise, praise what people do well. Then, they will be more accepting of your ideas for improving what they don't.

5. You can't thank your crew enough, so do so generously, often and with sincerity.

6. Try to never lose your temper. You may feel better at the moment, but later you'll wish you could take your words back. Nothing -- no matter how bad -- is worth humilitating someone else.

7. Directing can be a lonely -- but very rewarding -- business.

There's actually a great article on this site about directing that touches on this issue.  You never want to ACTUALLY lose your temper, because then you're out of control and will say things that are very damaging.  But if you do get really angry for a justifiable reason, it can be useful, once you've calmed down, to have a "fake" bout of anger, where you yell at people who need to be yelled at, and make them settle down, but you're always in control, and your "angry" words are carefully chosen to hit the notes they need to.  It's a careful distinction.