I think the main thing is: Just do it. Plunge in! Being Canadian, I go swimming in icy cold lakes, and there is always that dithering moment. "Am I really going to do this? Won't it hurt?" And at some point you just have to flop in there and scream. Once you're in, keep going. You may have to crumple and toss, but we all do that. Courage! I think that is what's most required.