This is one of the techniques I have learned through RPGs and LARP. It is a subject that actors have spent years to study: Immersion. It goes without saying that I’ll barely scratch the surface with this tiny article.
Immerse your self in a story and its characters and you will see that your audience will do the same. When a character in your story is doing something or saying something show it with your whole body, become the character. There are many ways and styles to do this, but most important is that you have done some preparations. As a storyteller you will have to keep track of many characters.
How to immerse your self? Study your tale and figure out the building blocks of each character. for each of them consider this: Who is she and what role does she play in the story? How does she walk and talk? Bad habits? What separates her from the other characters in the story? What feelings does she have? What feelings does she display? In short: How is her personality and how is her personality perceived? These are all important things to ponder and when you have pondered for a while try to put your self in her shoes. Act like her, speak like her, think like her, feel like her. Convince your self that you are that character!
My best tip to get inspiration on characters and archetypes is to study people out there. Go to a place where people are waiting, like a bus stop, train station or a place people gather, like a pub or café. Look for people that are a bit out of the ordinary, either because of how they look or how they behave, try to notice as much as possible about this person. How does she use her arms? How does she stand/sit/walk? Qualities of voice and language.. This technique has given me some very amazing characters and characteristics to use in my stories.
The tricky part with immersion as a storyteller is that you have to jump in and out of characters, rapidly and many times during a story. And it becomes even more tricky when your characters are having a conversation. There is only one tip I can give to help with that: Practice and experience.