This may seem to be silly advice, but BE SMART. That means don't let your emotions or ego rule you on the set -- THINK before you shoot off your mouth. Every action you take and every word you speak has to be a calculated move designed to make your film better.
As a first-time director you have your authority challenged on a hourly basis. Everyone's watching you and second-guessing you because they want to be where you are. On the other hand, they want the film to succeed, so they want to look at you and see confidence, honesty and commitment -- what they don't want to see is a selfish brat. Remember - they have never seen a feature film that you have made. They've never read a review of one of your films. Will the film suck? It could. And remember, they've probably worked on several films that have been awful. It's hard on an actor or crew person to work their ass off and have the film be horrible. They ask "Why did I kill myself for that piece of shit?" It's easy to see their point.
Remember -- it's ALWAYS the director's fault if the film sucks -- and that's the way it should be. It's easy to get bent out of shape when you feel you are not respected. But it's better for the film if you out-think people rather than just having an ego fit.
If the actor is challenging you -- remember he/she is scared to death that you will make them look foolish. Address that fear by doing whatever you can to help them trust you (knowing what the hell you are doing helps). They want you to lead them... and to listen to their point of view -- it's a very delicate balancing act.
In many ways every actor and crew person is your opponent in a negotiation -- your job is about negotiating them into your vision for the film -- which is where they really want to be anyway. Just remember that the only leverage a first-time director has is his/her brain. You haven't directed an Oscar-winning film yet -- so you can't bully anyone. The only power you have is the power that comes from passion, determination, wisdom and commitment. So get those things in spades before you step on the set!
SO, THAT'S MY TOP TEN -- I write all of this admitting that I love films and filmmaking (really!). It took me over twelve years to raise the money for my first feature film, and I feel very privileged to have been given my shot. It was only through sheer persistence, not being smart enough to give up and the grace of God that I got the chance to make my first feature. If you are stubborn and smart enough -- you might make it, too.
By the way... You'll notice I left out all that stuff about "raising the money" and "making the deal." It's all random chance anyway... so whatever I could tell you will be almost worthless because what worked for me will probably never work for you. What matters is that if and when you DO get your shot, you have the craft and vision to make a film that means something.