Naturalness & Sincerity
When you speak lines from a play inject as much naturalness and sincerity into your delivery as you can command. Speak the words as though they really express your own ideas and feelings. If you feel that you must exaggerate slightly because of the impression the remark is intended to make, rely more upon emphasis than upon any other device to secure an effect.
Never slip into an affected manner of delivering any speech. No matter what kind of acting you have seen upon amateur or professional stage, you must remember that moderation is the first essential of the best acting. Recall what Shakespeare had Hamlet say to the players.
Nor do not saw the air too much with your hand, thus: but use all gently; for in the very torrent, tempest, and, as I may say, whirlwind of your passion, you must acquire and beget a temperance that may give it smoothness. Oh, it offends me to the soul to hear a robustious, periwig-pated fellow tear a passion to tatters, to very rags, to split the ears of the groundlings, who for the most part are capable of nothing but inexplicable dumb-shows and noise.