Understand that as director, this is YOUR film. No matter how many other members of the crew dedicate themselves, fans are going to remember your name.
Despite this, directors can sometimes be biased when it comes to casting, envisioning actors in certain roles before the script is even completed. This is where casting directors enter, to remove the bias.
Meet with the casting director to go over the ultimate goals of the film.
After, schedule a meeting with yourself, the casting director, the producer and the line producer in order to go over the budgeted money allocated for the cast.
Based on the budget, the casting director, whose role is similar to that of a general manager in baseball, will determine how many star-level actors can be assembled.
Avoid watching the auditions live. Instead let the casting director, who will be much less intimidating to the actors, run the show, allowing you to watch via videotape when all is said and done.
Let your opinions be heard, but do not block out the opinion of the casting director. If he or she really feels strongly about a certain actor, it is usually for a good reason and should be taken into account.