The best way to overcome fear of rejection, be persistent and willing to try new techniques is to have a don't-give-a-shit-attitude. I know people with this attitude who have no game or knowledge of game, but if you combine game with this attitude your unstoppable.
You obviously can't carry this attitude into your living room and punch ur sisters friend in the face then pee on her. U gotta calibrate. Be polite, be socially acceptable (can't just walk outside with your cock in ur hand), but when it comes to cold approaches don't give a shit, I mean TRUELY don't give a shit. The type of don't give a shit attitude you have when your drunk, except you'l be sober and not reeking of alcohol and slurring your lines and falling down (extremely low value).
The only way to achieve this attitude is by conditioning. By going out to clubs with no knowledge of textbook game, and going up to the hottest girls and saying "hi my name is...." and being a completely AFC. Or even going up to them and doing ridiculous things you do on dares, like telling them you just got a sex change and want them to know if it looks good. But the point is to go up expecting to get rejected. If you do this over and over and over again for a couple months, when you start doing textbook game then your success will go through the roof.
PS here is the PERFECT example of this attitude... Phil