Lets see, I'll make a little list. This is form my own experiences, grades 10-11-ish. A bit of grade nine too.
- Listen to what you say.
- Ask a lot of questions about yourself, your thoughts, ect.
- Smile nicley every time she sees you
- Never leave abrubtly when you're near; without a good excuse.
- Give you compliments
- Do casual touching, (Hand-on-shoulder, quick hugs, sympathetic pats, ect.)
- Often ask about your plans, in the hopes that you two will meet up. (Dances are commonly used.)
- Tease you in a friendly way
- Say things about situations you two may get into, (talk about lingerie, mention things like "I'll let you look up my skirt if you help me with my project." None of them are serious, of course. The point is just that she wouldn't say these things if she weren't comfortable with you.)
- She will try to be around you a whole lot.
That's the basics. I don't know much about the body language, I've never had the intrest to study it before. I'm sure you could google it, if you were curious enough.