Going from Friend to Boyfriend/Girlfriend
First, this is a REALLY common situation. Many, many friends become closer and closer and then start thinking about dating. There are hundreds of movies about this situation. It's the ideal way to start a relationship, because all relationships should be based on trust, honesty and communication - something friends have built in. An ideal relationship is between best friends who love each other.
But it's hard to get started. Both people worry about risking the friendship, which is very important to both of them. So you want this to go quietly and smoothly.
Your aim is to have your friend spend more time with you, and to move from 'close friends' into 'romantic partners'. So you want to make this as smooth and non-threatening as possible. You want both you and your friend to feel comfortable with it.
So don't go leaping into a question like "Go to dinner with me at Le Chez!" in front of all of your target's friends :) If you're close friends, I imagine you already go out to movies and dinner, right? If not, that's where to start. Find a nice, fun comedy movie that you'd both enjoy and ask your friend to keep you company by going. Say you want to try this new restaurant in town and will your friend go along with you. That way you can test the waters with your friend and see how much you both enjoy it.
If these work out fine, just start changing the tone of those outings. Go to a romantic movie instead of a comedy. Go to a romantic restaurant instead of an Irish Pub. Instead of hugging goodbye, like friends do, give your friend a tender kiss on the cheek. Forget your jacket and borrow your friend's, or just stay close to keep warm. Give massages and backrubs when your friend feels tense or low, and ask for one when you're feeling a bit stressed. Nothing too blatant, but something showing you guys are close to each other. Build up that personal contact.
Your friend will either be uncomfortable if these changes are too much, or your friend will be happy that you are moving even closer together. If your friend is happy, then you're all set, and keep moving along!
Be sure to check out:
How To ... in Love