Callbacks are where the real casting happens. Callbacks allow you to see in real time how actors listen to each other, take direction, and make creative choices. Print off scenes for each character and pair up actors to see how they interact and the choices they make. If an actor is good with various people not only are they talented, but they are able to listen and collaborate well with others. Try to see as many different pairings as possible and your goal should be to see which actors make the boldest choices, listen and collaborate, and take direction. Once you have a good sense of the actors talent and skills, cast the most central character first and base your other casting decisions off of that choice. Always cast work ethic over talent, since talented people are often the laziest and most averse to critiques. Remember hard work always beats talent.