This will be a pretty large step for you it sounds like. I remember the first time I tried something on.. I was about 6 years old. Got caught standing in my older sister's room wearing a full outfit. I didn't mean anything perv by it... I just thought they were pretty and wanted to try them on lol.. Now when I look in the mirror as myself.. I remember them laughing at me. Crazy how something like that can scar you.
When you look in the mirror for the first time.. be nice to yourself. Don't create any bad habits and don't judge ANYTHING the first time. Or the second. Or even third. Just look at yourself and try to improve everything you see. Even the parts you might think you like at the moment. After a month or so.. you're going to look in that mirror and think "dayum I feel smexy today."
You're going to be your own worst critic. Be careful what you think of yourself when you see yourself. Hating the image in the mirror really is a terrible thing early on. I've been working on my femme side for about 4 months I believe.. and am just now starting to smile back at myself and think "yunno.. I can do this"
So can you!
I'm ALWAYS excited to try on my new things omg! I got a gift certificate for vic's secret from my older sister for xmas (the one who laughed my self esteem into a coma at 6). Can't wait to see what's waiting for me to try on in there!

Number one thing to remember when you're putting your new things on... HAVE A BLAST DARLIN!