In the past I have spoken about one of the secrets to being a good performer is to have confidence in your material and yourself. The audience can smell inexperience. (it smells like black licorice which is gross) One of the tells of someone who hasn't been performing long or not been trained properly is bad posture.
If you see someone who is doing a trick for you with slumped shoulders their body language denotes that of someone who doesn't give a flying fuck about what they are doing. Watch a confident seasoned performer. Their shoulders are back and they stand up straight (unless it's for dramatic or comedic effect). Look at yourself in the mirror. Does the way you stand give away more than you know? These are the tiny things you have to be aware of as a performer. Being proficient at the mechanics is just one tiny part of the puzzle.
For those who it does not come to naturally movement and/or acting lessons might be of a big help.
Odin knows it couldn't hurt...
PS: I will announce the winner of my contest soon.