1) Pack lightly- Most races that are under a half-marathon will not have a bag check, so you're going to have to carry everything with you on your run. Stick with the basics: safety pins for your bib (though these are usually provided at the registration tables), your car key (key, not keys), and maybe a pre-race energy booster. Most running pants and singlets will have a small pocket for your key. Other tricks include hiding it on top of a tire on your car (not recommended for urban areas), or using a key magnet. I also bring my iPhone and ear buds so I can listen to music. Some races don't allow you to wear ear buds. Check the race rules in advance.
2) Don't run in anything you haven't run in before- I once bought a cute running skirt with attached capris running pants, planning to wear it for an upcoming race. Fortunately, I couldn't resist wearing them for a quick run through my neighborhood, and discovered they were uncomfortable and had to constantly be adjusted. You would think I'd have learned my lesson. But it wasn't long after that, I bought a thing to cover my nose and mouth for running a 5K in sub-freezing temperatures. It kept falling down, and didn't wick the moisture from my breath, so it was doubly cold on my nose when it slipped down. I posted a horrible time from messing with that thing the whole race. One short run ought to be enough for you to learn whether a clothing or accessory item is going to work.
3) Three's a crowd- Especially when the course runs along a sidewalk or other narrow path. Running a race with friends and going out for coffee afterward is a fun way to spend a Saturday morning. But please run no more than 2 across, for the sake of those trying to get around you.
4) Move over- The first 8K I ran was this past winter in Greenville, South Carolina. There was a sweet, 14-year old girl running begrudgingly, with her family cheering her on. She would run and get ahead of me, then STOP. All of sudden. RIGHT in front of me. And start to walk. I about fell on top of the poor thing. After the third time, I finally chided her (and got a rude reply). Younger runners tend to be the worst offenders at suddenly stopping to walk or tie a shoe. The person running behind you will quickly become the person running you over, so it's in your best interest to check behind you, then move over to the right before stopping to walk, or bending over to tie your shoe.
5) Hydrate- the day before. If you wait until the morning of the race, it'll be too late. By the time you go to bed the night before a race, your urine should be almost clear. Make sure you're replenishing electrolytes, and don't drink more than 32 ounces of water an hour, less if you're one of those skinny people, to prevent water intoxication. (No, I didn't make that up. It can really happen, and it can be fatal.)
6) If you must spit, go to the right- I don't know if this is an official unofficial rule for running road races, but it should be. I don't enjoy dodging spit bombs in the middle of the road. At least be mindful of people around you so they don't run into your mid-air loogie.
7) Water Station Rules- Even a 5K will have at least one water station. They're usually going to be on your right, but not always. If you're going to get water, move over to the side and get some water. If you plan to stop and chat with the volunteers at the station and catch your breath, get out of the way of those runners who want to grab and go. Typically, a volunteer will had you a small cup that you grab while you keep running. Take a sip, and toss the cup on the ground. No, really. It's okay-- but only during a race. A couple of things to keep in mind: A) There are other runners behind you. They don't want to wear the water or sports drink that you're tossing; B) Be careful merging back into the course so you don' trip up the runners who aren't stopping.
8) Post-race food- Nearly every race provides a post-race snack for the runners. You'll never know what these are going to be until the day of the race, and there's no guarantee that there will be anything left by the time you get there if you're a slower runner. It's a good idea to have a recovery bar in your car just in case. Keep in mind that what your body needs most to recover from exercise is protein, and most post-race food would actually be better pre-race foods-- lots of carb-loaded bagels and bananas. Remember-- the food is only for the runners. You're cheering squad needs to bring their own snacks.
9) Pre-run the course- Especially if you're a new runner, it's a good idea to drive the course, and then run it so you know what to expect. I've only actually done this once, and only because I was going to be running a relay and the team captain insisted that I run it with her. I was glad that I did, because there was a hill that would have caused me some panic had I not been prepared. If you're just running for fun, it's really not a big deal. But if you're looking for a PR (personal record), you definitely want to do a practice run.
10) Be grateful- No race would happen if it wasn't for the people who volunteer to do set-up and clean-up, hand out water, and direct you along the course. There are usually police officers blocking traffic to keep the roads clear and safe for the runners. Give them a little shout-out as you pass by so they know that they're efforts are appreciated.
What are some things you've learned that a new runner might want to know before they head out to their first road race?