Just...don't talk! Ignore them! Treat them like trash! They will love you and never let you go. If you don't want her anymore, tell her you're in love with her. She'll dump you for another one in no time!
Don't send ur cock pic for start an conversation and act like you're chatting with a your friend, all you need is don't act weird and you're ready to get da bitches.
Serious advice: be yourself, be confident and love yourself more. From my personal pov, I love confident but respectful guys. Just be a little confident but dont be too weird, and if she doesnt want to continue the conversation with you, just give her space and move on.
Just be confident without acting like a dick. Then some small things like eye contact, show some smile etc. Believe in yourself and just relax. Topic depends on the moment.