Don't skimp on gloves, and if you're not going to wear riding pants, wear heavy blue jeans at the least. Most of us have gone down before, and I have yet to hear anybody say, "man, that was fun...let's do it again".
I just went down the other day in the rain. It sucked. I came out with some minor road rash and a body full of scabs. I was wearing my usual Dockers slacks and they look like shorts. My body took the blunt of the fall, and even wearing a jacket, I was still scraped up through friction and abrasion.
Your hand is instinctively going to be your first defense in preventing a crash/body injury. Make sure you buy quality gloves that cover your wrist.