I agree with all the above, flirting is about practice until it becomes instinctive.
I'm still learning but for me its about sinking into a Mindset where I take nothing seriously and just relax and be confident around women.
Flirting is not always about what you say but about your general demeanor and vibe. As a stating point you need one thing: innuendo!
you can turn the most mundane topics into sexual ones with a quick sexual pun. It can be anything, just throw in words like, hard, wet, throbbing or mention her being flexible.