An example I like to use is when I was 16, my brother took me to a bar. He said, "Just walk in thinking, 'Bitch I OWN this place,' and people will think you belong." I've been following that advice ever since because it works in most situations.

Confidence is important important in roleplaying. Even if you don't really know what you are doing, if you just act like you're really good at it, then a lot of times people can't tell the difference. So I would say just make it up as you go along, pretend like you "own" that roleplay, and you should be good to go. Confidence is easy to fake, and since it is his fantasy I doubt you have much to worry about embarrassment-wise

Practice makes excellence... Like the first time you swing a golf club or put on roller skates, it's going to feel awkward and uncomfortable at first. The more you do it, the more comfortable you're going to feel. I don't recommend going to work or the grocery store wearing the costume, but I do recommend trying to "think" like a naughty nurse all day long, BEFORE you even put the costume on. If you practice/pretend long enough, you will own it as Taylor describes because it'll become second nature to you.

Every woman has a naughty nurse or dirty cop or whatever inside of them. When we were kids, we used to play pretend all the time. As we grew up, we somehow forgot how to play pretend and how much fun it is to be creative and use our imagination. You'd be surprised by how much fun you'll eventually have when you realize what an escape it becomes.

it's so much fun.

but if you are having problems with it, think of it as dressing up for halloween and adding a bit of acting to it. that may make it easier for you.

Do you have issues with the roles, or are you just not comfortable with roleplaying in general?
For sure get yourself a sexy nurse costume, and dress up while he's out. See how hot you look and it will help you get in to character. Roleplaying is grown-up play time for sure, and it's the time to pretend and really let loose. For me, it really helps if we have some dialogue while we're in costume. It tends to be a little awkward if you just walk into the room dressed like a nurse and you start having sex. If you walk in, and talk about what's making him feel sick, what you could do to make him feel better, you can both get into character a little bit and pretend to be nurse and patient. I also find that that dialog time tends to diffuse the discomfort as well as make the situation more palpable.

I've never really done roleplaying, and that's what makes me uncomfortable. We have played around with it a little bit without costumes, and it was a lot easier than I thought it would be and it was awesome! I think that more than anything I'm too worried about my body and not turning him on with it (which I know it totally silly 'cause he REALLY wants it). I do need to get one and just figure it out. We have a great sex life and I know this will only make it better, I think just the idea kinda freaks me out because I don't want to disappoint him.

My boyfriend & I tried roleplay once...pirates, of course, but we both we smiling and laughing but we were having fun. I think that's a big part of making it great. It's awesome when you can do it without cracking up, but practice makes perfect, so until then, just have fun.

You could always practice roleplaying in nonsexual situations- costume parties, acting exercises/games, even Dungeons and Dragons.

It seems to be a inicent enough fantasy, its not like he's asking you for a threesome or moresome. Get a costume that you feel sexy in and let your imagination take it from there. Now he owes you one of your fantasys.