It’s pretty simple: if you see an attractive girl, go talk to her. If you like talking to her, ask her out.
If you continue to like talking to her and going out with her, continue this until you marry her. If you don’t continue to like talking to her and going out with her, tell her you’re not interested anymore; no further explanation needed.
But don’t stare at a girl you like. Don’t ignore a girl you like. Get the job done and move on.