Self-aware, sensitivity to criticism, anxious, uncertain of themselves, difficulty with self-expression, are things that come to mind.
I think trouble with criticism could be one of the most common factors among shy people--keep in mind I don't speak for everyone, though.
What to do about it? That's something I don't believe I can help with.. I've never been on a date, or anything like that. Doesn't mean I'm not interested in girls.. far from it.. it means I'm too overwhelmed by everything involved with meeting a girl.