I think I'm not being nearly persistent enough when going after women.

The long story is my dad was a salesmen and never took no for an answer and it annoyed the living hell out of me when I would be telling him something and he would act oblivious to it. So now whenever someone says no, comes remotely close to saying no, or even if they don't say yes, I just stop what I'm doing and go talk to someone else because I don't want to be that annoying guy that doesn't know how to take no for an answer or when they want me to leave. Plus I'm kind of uncalibrated as to how hard I can push before I'm being annoying and inconsiderate.

Anyone have any ideas what a guy could do about this? How do you know when a girl means no or means "try harder?"