the only thing I can tell you is not only to practice but also find people around you to inspire you. take one of my friend for example one of my classmates who inspired me to start painting. The best talents improve your talents.
I liked him more with the original nasally voice than the demonic voice. It just fit the "surprise I'm a douche bad guy" situation more than the ominous "You know I'll be the main boss at the end" voice.