Tactic 0, smile and say hi to yourself in the mirror 100x to build up the confidence to do it to someone else

I think you're half joking, but if you have that much difficulty then yes, absolutely unironically practice in whatever is a safe enough environment until you're ready to take on the real world. Practice in a mirror, practice on your family/room-mates if available, watch the interaction in videos, whatever. It's an actual skill, and like any other skill it can be done through sheer massed practice even if you start from virtually zero ability.