First of all, read your script. Note what your character says about himself or herself.
Is your character -
Bold or shy?
Caring, or careless?
Happy, sad or angry?
Rich or poor?
happy with their job / lifechoices?
Married or single?
If married, is he or she happy in that marriage? Why? Why not?
What is his/her profession?
happy with their job / lifechoices?
Married or single?
If married, is he or she happy in that marriage? Why? Why not?
Is anything mentioned about his or her past? How would you imagine that would relate to how he or she is feeling now?
Get as complete a picture of your character as you can – for example, a 17th century whore in a country town, would be played markedly differently from a 21st century call girl in Hollywood, or a Celtic chieftain from a modern day monarch, or a 16th century witch, would be a very different person to a modern day neo-pagan/witch.
This is now where you must take into account the society in which your character lives. Take into account the history of the time in which he or she lives, and the society that he or she will have grown up in. How will that affect the character? And their body language? The modern Hollywood call girl would wear high heels, the 17th century whore would not. Therefore they would walk differently..
The Celtic chieftain would be a lot more rough and ready than a later monarch, and the 16th century witch would be mortally aware that if caught she would be burned at the stake, whereas in the 21st century, she would have no such fear.
Even in the modern day, depending on the culture, your character will be affected. A hippie would be different from a business person, and a Japanese girl would behave differently from a British girl.
Now, based on the character as depicted in the script, and what you have found out about them, create a little story about them, and rather than considering them to be someone apart from you, you now must imagine yourself to be that person.
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How do you feel in certain situations? (This is where the method acting comes in, to draw upon your own past experiences and feelings, to understand how your character might be feeling). What are the differences between what your character is feeling, and what you are feeling? Why?
Take an hour each day or so, to walk around the house as your character. It’s hard at first and becomes easier, don’t worry.
As soon as your costume is available, you are welcome to wear it during rehearsals – very often people find that dressing as their character helps them invaluably.
Sometimes, when a character is far removed from how you are yourself, it can help to watch a movie or TV show with a similar setting, or similar character to yours. Watch that character. How does he or she act? This can give you some pointers to start with. If you are unfamiliar with the historical period, or culture, get a simple book from the library, even from the kiddies section (sometimes these are better as they are heavily illustrated!). It does not have to be anything complex, in order to give you a overview.