Casting can make or break any story. Ask yourself what each person can bring to their characters?
Make sure the people your cast are aware of what they getting themselves into. You need your cast to be punctual and reliable. Think about how much time your actors will need to devote to the project, and make sure they are confident they will be able to give you this time.
Think about advertising your auditions through local drama groups and through schools. Give everyone a chance to read the script properly before they audition and don't be afraid to give direction.
Rehearsals
Rehearsals are a chance for your actors to get to know their characters. Seeing your script performed is a perfect time to spot and fix problems before you start shooting.
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For all the filmmakers out there, read advice on holding auditions here