Follow someone that knows where they're going.
No matter how cold you are before a race, only wear a short sleeve jersey whe you go to race. I learned this to my peril when during a winter alleycat I wore my raincoat and nearly melted while cycling. Had to take the thing off or I wouldn't have finished the race.
Don't believe what other racers tell you. While this racing thing is mainly for fun, you can't trust anyone!! People will try to throw you off the scent to gain a few seconds on you, which is fair enough, if you don't know where you're going, that's your tough luck, hence point 1, follow someone who knows where they're going.
Piss before you race. Squeez it out of you!! Nothing worse than those few pre race beers catching up with you mid race and cramping you up.
Carry a map. **** street cred. I've been doing this job over 10 years and I still carry a map, 'cos you never know when that blank is gonna come screaming on you and a place you visit 20 times a day could be on another planet for all you can remember.
Lights, helmet, pen. While I don't use a helmet in work, I also don't take the risks I do when I'm in an alleycat. Adrenaline I guess, but you can pay for that ****, so better safe than sorry. You can always take it off for the post race photos... While lights aren't gonna stop a crash, at least you can comfort yourself with the fact that 'I had lights, I can't believe he didn't see me!!!' Pen, well you never know what these checkpoints are going to throw up, and if you don't have a pen... well you're not gonna get much work done if you're a messenger, so you may lose out in a messenger style race.
Have fun. When all is said and done, all this **** is about having fun. It's why we ride our bikes, it's why we're on this forum. Ride fast, ride safe. some of the greatest stories of my life have come from alleycats and i want that trend to continue, for me and everyone else that takes part.
Oh, and in case I didn't stress it enough, follow someone who knows where they're going... and then outsprint those dumbasses in the final straight...
Enjoy!!!