Asking a girl out isn't particularly difficult, but it can seem that way. If you want to ask a girl out but you don't want to risk face-to-face rejection, you can shield yourself by writing her a nice letter. This can help you express yourself without succumbing to nerves and also show her how much you like her and want to spend time with her. The key to a sweet letter is that you be honest, true to yourself and make sure you express yourself clearly.
Jot down a couple things that you like about her that are unique to her. This will make your letter personal, which will in turn make it more sweet.
Focus on a couple of the qualities from above. Your letter should be short and sweet, and if you focus your energy on fewer qualities you will come across as more authentic.
Be honest in your letter. You should tell her exactly how you feel. Don't go over the top with compliments, but you should clearly say that you like her and say why.
Be yourself in your letter. If she finds you funny, you may be tempted to be really funny; if she thinks you're nice, you may be tempted to be extremely nice. Don't do this, though -- you'll seem insincere and she will not be as enthralled as she could have been.
Ask her on a clear date. Rather than "let's get coffee sometime," say "I'd like to buy you a cup of coffee at . . . " If you put a specific time and place, then it will be easier for both of you to follow through.