In the set scenes we see Malvolio acting in a very arrogant and self-important way towards Feste, Maria, Sir Toby and Sir Andrew. This makes them decide to play a trick on him to teach him a lesson.
When Malvolio arrives, Sir Toby, Sir Andrew and Feste are up late at night singing, dancing and drinking. Maria comes to tell them to be quiet, but does not seem very angry. Malvolio's attitude is completely different. He asks if they are "mad" and says:
"Have ye no wit, manners, nor honesty, but to gabble like tinkers at this time of night?"
I would direct him to burst in looking dishevelled and furious, but speak in a stage whisper, emphasising the insult "tinker".
Instead of letting the others defend themselves, Malvolio then continues in his tirade. He accuses Sir Toby of turning Olivia's house into "an alehouse". He calls her "my lady", as if they have some special bond, and accuses the others of having:
"no respect of place, persons, nor time."
I would direct him to change his tone slightly, sounding self-important and smug. He should have a sneer in his voice and a very superior expression.
It is clear from the way Sir Toby reacts that he doesn't take Malvolio very seriously, so Malvolio now tries to threaten him. He says that Olivia has given him a message to pass on:
"though she harbours you as her kinsman, she's nothing allied to your disorders."
He continues by saying that unless Sir Toby mends his ways, Olivia will ask him to leave the house. I would direct Malvolio to smile when Sir Toby makes fun of him, and then speak in a clear, deliberate way so everyone can hear. He should use a sarcastic tone of voice, as though he is speaking to a naughty child.
Now Sir Toby seems really angry. Firstly, he and Feste sing a song making fun of Malvolio, but then Sir Toby turns on him. He says:
"Out o' tune, sir: ye lie. Art any more than a steward?"
Then he tells Malvolio to "rub [his] chin with crumbs".
I would