A: Some times you just don't realize it but say when a guy sees a girl he will smile. But this is so subtle it can be taken as just a friendly smile. Some people don't even realize it when they are doing it.
A: Become flirty: 1. smile at him, and when you see him 2. call his name and smile and wave 3. touch him appropriately, Like walking by on the arm.. little things like that.