1. Remember, you don't always get what you want. When you're writing your script, you have a specific person in mind to play the part, but you're going to have to settle with someone else that may be different looking, or acting. It happens. Get over it.
2. Be believable. You don't want to see a fat red-headed guy that hasn't showered as a jedi master.
3. Be believable again. Make sure couple has chemistry on camera. You don't want the audience to say, "What? He would NEVER be with her!"
4. Always feed your cast. A hungry cast is an unworking/unhappy cast.
5. Don't be too pushy. Don't yell unless completely necessary. Don't knock others performances, at least not to their face. Be nice. Let them show you their interpretation of the character. Take suggestions. Spielburg and Lucas took almost all of Harrison Ford's suggestions, and look how the Indy series turned out.
If you really want to choose between lots of people, hold a casting call.
Post a message, or run an ad. You can cast by appointments, but make sure you see everyone.
In your casting notice put the following information so there is no doubt what you want...
What days and times casting is being held, if it is a cattle call or audition.
Pay or no-pay, you will recieve copy, food, and credit. Most actors need to create a reel so this pays them without paying them. Plus, if you don't feed people they get cranky.
If you will be requiring any nudity.
When doing casting, give the actors a form to fill out. This will give you an idea of what they are like personality wise.
Some examples of what to ask:
Name, gender, whether they are over 18, contact ph#'s, e-mail address, availability: days and times. Clothing size for both men and women, style of clothing they posess, what color are their clothes. What they are not willing to do. Ethnicity, their strength and witness.
Also, video tape the casting sessions so you can refer back.
