What are some Do's and Don'ts when approaching a girl in public for the first time?

I was thinking about my past relationships today and how I've dealt with introducing myself. From what I can gather from memory, I've always either had myself introduced by a friend or have introduced myself through conversations online. Now, this was great when I was younger, however I don't want to have to rely on anyone besides myself or having to quickly swipe through tinder to strike up a conversation if I so happen to see a certain woman who peaks my interest as "Ms. right" lol. What are some do's and don'ts for approaching a prospective girlfriend in public? Ice breakers for different settings (some for the gym or college would be nice since that's where I spend most of my time in public), body language, etc. Also, please don't copy and paste any of the crap from pick up artist. Their advice is generally awful. I'll be looking forward to your replies :D