My best tip is to get used to the idea of being wet. If you wear a poncho, you'll be marinating in your own sweat. If you don't, you'll be soaked with rain. I have a strong personal preference for the latter, but some people seem to prefer the "thanksgiving turkey in an oven bag" method. You'll have to figure out what works best for you.
Another thing to consider is footwear. I prefer flip flops or
Crocs. If I wear socks in the rain, I will have a dozen blisters by the end of the day. For other people, it's the opposite.