2. Ask the name of the dish
To be honest, it isn’t my method, I stole it from one guy, who did it and it was impressive. He came to the canteen, saw one girl sitting by her own and eating a tasty dish and then just ask how to say the name of her dish in Chinese and what exactly it is. After 10 minutes he came back to her holding a plate with the exact same dish and asked if you could sit next to her. And then they just talked about everything.
Make a note, no matter what café or restaurant you go to, you can go to the person you like and try this method. There is nothing to lose here, even if conversation doesn’t work out, at least you can discover a new tasty dish.