90% of directing is casting. That's the first thing I'll say.
Next...set up some rehearsals, and see how things go. Work with your actors, talk to them, discuss character, wardrobe, etc...however, I will say this...don't OVER rehearse. That is the bane of some films I've worked on--this isn't stage. You want a natural energy and (I'm going to say it) an ORGANIC feel. Often times when you over-rehearse, you'll kill that organic tone.
On set you can be as directory as you want...if an actor messes up thier lines, blocking or whatever bigtime...you don't always need to cut and start from 1...you can stop them (while still rolling) and say, 'pick it up from [so and so line].' Just be quick about it, as you're shooting on film. Good actors should be prepared to do this anyway. You're shooting on film, so time is money, takes are money...try and make each shot count. Let the scene play through if you can, and fix it in the editing room. Make sure you get enough coverage and always get a safety.
If your actor isn't giving you what you want on set, and your direction between takes isn't working...take five, and pull the actor aside and discuss what you're looking for. Try and be creative with your direction, don't always go 'on the nose' with what you want. Sometimes actors respond better (or at least read better for the camera) when you give them something else to ponder while they are doing the scene (ie. instead of saying 'you're scared to death', it might work to say, 'in this shot, pretend like the room is freezing cold.') That's just a silly example, and it may not always work, but that's what it means to be a creative director.
Basically you want to let your actors run with their choices...until you aren't getting what you want. Then you can jump in with some direction.
Also, after each take, it's a good idea to tell the actors what you thought...you don't have to stroke thier egos...but a simle 'that was good...nice work...let's do it again.' The worst thing you can do after a take is not say a word and ignore the performance. Actors are insecure for the most part, and we like to hear something...anything, after a take. Feedback is good.
Good luck.