There are some things an actor must do, and others he or she must never do. These behaviors would fall under the topic of "Protocol" also known as the way one should behave. Doing the wrong thing can get you on some one's black list and an actor never wants that to happen if he or she wants to keep working.
It is easy to make a mistake, so we need to pay attention to how things are done. First of all, you must remember names, faces, and positions. I confess that I once forgot the name of the producer of a film I worked on. Interestingly enough, I never worked for that company again.
As a beginning professional we have to watch out for other things that could get us in trouble. Directors chairs with names on the back that are placed on the set are for those people ONLY. Do not sit in them. Ever. If you want to get on the good side of the director or assistant director (equally important), make sure that you obey their suggestions without hesitation. Being willing to do what is needed for the scene is of utmost importance.
Do not bother the stars or featured players unless they are between takes and relaxing. If you interrupt them when they are in conversation with the director or another actor, you could be determined to be a nuisance and lose your job.
Then there are the things you are supposed to do such as be on time for your calls. If it says five am for costume call. Be there at quarter to five. Once your position in a scene has been set, do not change it between takes. Always keep the same positions so the takes will match. If you are on the star's right side in one take and on his left side in another, it will be impossible to use both takes since they don't match. It is important that you always match your position and posture from take to take. Always keep acting until the director yells, "cut". Your dialog may be over, but the director may want the other actors' reactions in the take as well.
Keep your eyes and ears open and make sure you are doing the right thing at the right time. That is meeting your protocol as an actor.