Read through your selected monologue as many times as you need and write down notes in a notepad that have to deal with the parts of the monologue and what the character does. Is the character asking something from someone? Is he teaching or interacting with other characters?
Continue to dissect the monologue. Using your list of causes, now write down the effect it has on the situations in the monologue. If you are teaching someone to do something, how has this character reacted to it?
Make a note of the presumed emotion of your character as well as the others in the scene that are directly affected by it. This will become crucial to finding your emotion.
Make note of any actions that are being conducted in the scene. Actions can affect how your emotion changes.
Look at those verbal cues that can generate emotion, using your list of notes. If your character is asking something, instead command or demand it--these are different emotions that you can use to propel the monologue forward.
Look over the reactions the characters have. If you are politely asking someone to do something and they politely do it that is too easy. You have changed the asking into something more fervent--a command. How would you react to someone commanding, ordering you to do something? Using that information you can now create an emotional reaction for the next line in the monologue.
Consider your actions. Actions can increase emotion or change accordingly. If you are opening a door or drinking water you would do them normally. In an emotionally charged monologue you would slam a door and chug the water or forcefully slam the glass down.