I've thought of that problem, since the girl I've started going out with never has her hair down..
Haven't tried it yet, but this is what I've come up with, look into her eyes, smile, if she does the same then you're on the right track. Brush a bit of hair out of her face and behind her ears if you can, if not then just gently down the side of her face I suppose, the aim is to get your hand on the side of her neck. Basically, if she is still smiling and not pulling away then slowly move your head closer and do it. Thats what I'm planning to do pretty soon...