
Flirting is a subtle back and forth with a light hearted undertone. It can be ambiguous and it can be playful, you need to catch certain things said to you and find opportunities to insert your humor and display your personality to them. If its going well it creates tension that can be built up or broken in the right situation
Flirting to me used to just be how many of side jokes and memes we could remember each other liking and making callbacks to said jokes at the right time to get the perfect laugh and make them smile in a way no one else does. Kinda like being a good comedian who only loves one person in the crowd.