I always tell people who get embarrased about rp'ing to take it in four easy steps:
1) roleplay your character just like yourself, what you would do in that situation.
2) roleplay yourself turn to 11. exagerate all of your natural reactions.
3) roleplay yourself drunk. no inhibitions and think at the top of your mind.
4) roleplay the opposite of yourself. The hardest part and the one that requires acting skills.
I also advise to speak normal. NO "thee" or "prithy". just talk normal. like in forgotten realms or something. this is how i learned to roleplay anyway.