Rejection is kind of like stepping in dog poo. It's only going to get you down if you let it. Just scrape off your shoe and keep moving.
I know that this is a some what simplistic view, but it's the only one I have. You see, I was blessed with a father that instilled the "the only wasted day is a day you don't learn something" mentality; a mother who truly believed her children were exceptional and anyone who didn't think so too were stupid; and a sister fought her way tooth and nail to be the best at whatever she choose to do. Talk about good examples for a child.
That's not to say that all rejection to me is water off a duck's back. It's just that I understand that I am the one who gets to choose how I cope with it. I can either curl myself up in the fetal position and bawl whilst stuffing twinkies in my face, or I can wo-man up and move on. Besides, just because one person didn't like what I wrote/created, dosen't mean that no one will. That just wasn't the right person to go to.
I think it helps too that I do SO MANY things. You know what they say "jack of all trades, master of none"; that's me. I always have something different to go to to take my mind off of the rejection, to move on to. Children's story rejected by the publisher? Paint something. A gallery didn't like my painting? Sew a quilt. Quilt wasn't let into the quilt show? Make epoxy-resin jewelry. Visious circle, but it works for me. By doing something "new" I can remove myself from the sting of the rejection and when I'm ready to go back to it, I've moved on, it doesn't bother me anymore.