Things to remember...

1. No role can stand alone. Without every single person in the cast (and the crews), the show will be flat and without texture and not worth doing.
2. Your role is what you make of it. You can have 99% of the words in the script and bore the audience to tears. Or you can have 12 words and be the most memorable character in the show. 
3. You are not your character. You are the actor best suited to play that character. If the role calls for a ditzy blonde, a good actor could play that role even if they are a totally genius brunette in real life.
4. Be kind and supportive. Tearing down your fellow cast mates won't get you a better part. In fact, it will get you thrown out of the show completely.