What should you doIf you have a girl who is your best friend and she leans her head on you shoulder and stuff like that?

Is it friendly, flirty or sisterly? Girls are slightly more inclined to lean against you or hug you or whatever, but you should know her well enough to tell whether it's common for her to do this with everyone or only with you.

If she's your best friend, she could feel close enough to you to be siblings; alternately, she could be trying to suggest she wants something more.

If this is common behaviour for her, it's probably just how she is.

If it's unusual, or if you think it's more than just her being comfortable around you, try talking about it with her - if she's hinting at something it'll probably become obvious during the conversation.

If you're insanely brave and willing to risk it, you could kiss her to find out - but this most likely will result in a slap or punch in the face and you losing your best friend if you got it wrong, so... yeah, maybe that isn't such a good idea...