General answer, just walk up and talk, what you talk about depends on the setting. I can give examples but every situation is different. Here is how i met my boyfriend now: I was at Starbucks and noticed a guy looking at me while I waited for my drink (vanilla latte). I smiled and looked down. He walked up and said he was thinking about a dessert and what would I suggest. I suggested one (banana nut bread) then they called out my drink. I smiled and said bye and he did too. A couple weeks later, he was two people ahead of me to order. After he ordered, he stood near me and said "vanilla latte, right?" I said yes how did you remember that. He said, stand with me, it will be ready in a minute (ie he ordered it for me) so I did and then we sat together, I gave him my number, he called I accepted and it goes from there.

How romantic