How can I approach her?

I really like this girl but we have no cles together. We know each other because in middle school we had a cl together, and we have a fairly similar friend and even hang out with some of the same people( just at different times). I'd really like to talk to her but I don't know when to approach her. Every day after school lots of people meet in the courtyard and she's usually there. There were a few occasions after school where we saw each other after school with our mutual friend. Every time (at least 3) she complimented my sweatshirt that I made, and said she liked it very much. On Friday I saw her twice throughout the day and she waved and said hi both times. I feel as if I could talk to her about deep things but I need to get know her first. I really like her a lot and I might get nervous