How do I subtly flirt/flatter with a shy female friend? I would like to complement her a little bit, after a month I'm going to ask her out?

Our small social group just broke up and were getting used to talking one on one. We would only really talk while in a group. I would like to subtly and lightly flirt with her for about a month while we get used to talking with each other. So that after a while I can ask her out. That way she will hopefully have gotten the hint by then that I like her and she won't be surprised when I ask her out
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Any suggestions on how I can start making physical contact with her more?
How do I subtly flirt/flatter with a shy female friend? I would like to complement her a little bit, after a month I'm going to ask her out?
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