I am an introvert who freelanced for a while and now I have a permanent gig which includes biz dev. Former colleagues helped me by either letting me practise on them, or giving me helpful and motivating feedback, or by introducing me to possible leads. When I go out looking for leads I set myself goals for numbers e.g. 30 leads at such-and-such event. I find it helps to stop me from giving up and sneaking out early. I also took to heart the advice that it's better to get to an event early and be warmed up before the numbers get too daunting. I still suck at it, but I get by.