Any ideas as how to approach shy girls?

I heard shy girls are the hardest type to approach…if you can get a shy girl, you can get any girl. Supposedly, they’re hard to read and hard to make progress with, which I strongly believe in both. When you’re talking with a shy girl, you can’t tell if she’s interested at all…or at least it’s difficult to. If you make a move too assuming, she’ll clam up and shy away. So how are you supposed to read and approach her? I’m not sure if she’d want you to come on direct (since she’s shy and you complement her), or if she’d rather you approach her indirectly. Or perhaps something else entirely?

Anyone with experience, please share.
Anyone without experience, give me your input. It’s appreciated.
Any female that considers herself shy…your input would be awesome.