If you're not a real chameleon of an actor and if you're not one of those guys who can really shape-change themselves all the time one of the ways to keep pushing yourself and keep changing is to be in different kinds of movies.
When I was 11 my friend's mom made a peanut butter sandwich. I ate the sandwich and was like 'I'm never eating anything else again.' And I still eat peanut butter every day. I would put peanut butter on a steak.