There are three main things to consider: body posture, touch and facial expressions.
Of course, you have to know what to do when you want to make your intentions known to a woman you've just met but if she hasn't rebuffed your advances, pay attention.
She’s most likely into you if:
She keeps moving closer to you.
Even if you’re virtually breathing the same ear, she’ll keep scooting closer to you whether using the bustle of the crowd as an excuse to be as near to you as possible.
She constantly touches you.
This is where you need to give extra attention. If she touches, squeezes and her hand lingers- you have a chance.
She laughs with you.
Even when you’re not that funny.
She’s smiling a lot.
And generally seems happy to be in your space.
She’s in your line of sight.
If she’d rather sit beside you and cuddle or sit ahead of you and flirt back, she’ll want to be the centre of your attention and she’ll do it in subtle ways.
When she does all or most of these things, you should probably ask for her number and ask her to dinner or to an event you’d both enjoy soon.