Why would you want to limit yourself and not get any formal training? Training can lead to experience, which can increase your casting opportunities, which can increase your chances of success.

You have to audition for parts. You cannot just walk off of the street and ask for a part and get it. Drama classes are very helpful. After you have done some things in school, try out for local theatre groups. Start building yourself and your resume. It will help you far more than hurt you.

If this is what you Truly want to do with your life, then you owe it to yourself to do everything you can to develop as an actress. That means that you should take the courses, because in the end, you need to know as many aspects of acting as you can. In a casting call, that can make all the difference in the world. So do not short change yourself. Good luck!
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If you see an organization that you would like to help, but don’t see a volunteering opportunity posted by that organization for a group, it’s okay to call them and say you would like to volunteer as a group — they may have opportunities they haven’t posted. Also, many organizations are open to your own suggestions for volunteering activities.

If you want to do something that is representative of your club, many senior homes would welcome short skits and lively monologues.
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You Will find information here about "Los Soles Truncos" from Rene Marques. Excellent Play.

Good Luck with your project.
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to answer your question the top four are as follows (trying to put them in order of importance though some disagree).
scene study. this is the base of everything. you need to know how to take apart a scene and performs it. there are various techniques, adler, miesner, etc. this is essential because it will not only teach you acting skills but also how to approach a part/scene.

-cold reading. cold reading is basically learning how to audition when you have no or little time with the script beforehand (thus a cold read) . this is important because you need a good audition to land any part.

-a commercial class. people think this is important because as a beginning actor you’ll get work in commercials to start with. this will leas into bit parts in tv or movies. its not really essential to become a great actor, but it is to have an acting career.

-improv. improv looks great on a resume. in auditions it isn’t unusual for a casting director to tell you to improv the rest of the scene. also, it really teaches you how to be comfortable with your body and movements, which translated in your craft.

most classes let you audit before you pay for a 4-10 week commitment. this means you’ll get to sit in on one class. different schools/coached have different rules about auditors participating. some will just let you watch while others will invite you to jump in. either way, it gives you an idea of what the class is like.
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