If you are to portray a well-known historical character, read everything you can about the man. Perhaps you will have the fortune to come across a detailed description by one of his intimate friends.
If the man you represent follows any particular trade or calling, try to get acquainted with some such men. Take, for example, a foundry hand. Get permission to visit a foundry; go there several times, till the significance of the work is borne home to you. You will eventually realise not only what the men look like, but the way they feel, and will be able to suggest the way in which they toil. Tinker, tailor, soldier, sailor, rich man, poor man, beggarman, thief. What a drama of characterisation the line conveys; each is stamped with his trade or condition.
Go again and again to life; let your body and brain reflect it. Make your types actual.
A Parliament, a Court, a ward of a hospital, with its quiet doctor going from bed to bed. The deck of the steamer, the interior of a bus—they each become a school where valuable lessons may be learnt.
Unless you suffer from very definite physical or vocal limitations, strive not to get grooved in your work. Do not repeat yourself over and over again in each new part that you play.
Remember that the number of types in the world is infinite; that the playwright is always striving to present to the public some new character.
Ever add to your knowledge, and recollect that work is life's great recompense. Thank God your toil is endless.