I'd just like to add that one way to really show character emotions is to describe scenes just as the character would. This works even for third person (I believe there's a name for it, but I can't recall it as of the moment...).
"I'm so sick of my parents telling me what to do all the time, running my life as though I were some kind of puppet-doll they could manipulate. I can't even talk or express the way I feel without my mother interrupting my every word, or my father patronizing me with his scornful taunts. To heck with all that! I'm finally eighteen, and I'm looking forward to saying goodbye forever."
Keep in mind, too, that the degree of physical reactions will vary from character to character, depending on their different personalities.