I don't think it matters how often you race, or whether you're racing for fun or trying to place. I believe that everyone has some sort of pre-race anxiety or jitters. I know that I still get nervous, regardless of what my goal for the race is. Many people have different rituals that they follow or good luck charms that they carry with them. I don't necessarily have any of that, but I do have a pretty basic routine that I follow.
During the day before most of my races, I try to get a light workout in. If I'm doing just a running event, then I'll get a very short run in, maybe a couple of miles. If I'm doing a triathlon, my light workouts have been going on for a few days. Basically, the day before a race I try to relax and stay as low-stress as possible. I try to eat meals that are on the lighter side (not necessarily smaller portions than normal, just not heavy meals). For dinner, I almost always have some sort of pasta and sauce, and I've learned the hard way to eat a smaller portion than I normally would for dinner. I try and have dinner a little earlier than normal, and head off to bed with plenty of time to sleep.
Sleeping is a tough issue because it's almost near impossible to actually get a good nights sleep. Some people take NyQuil to help them sleep, other people will take other over-the-counter medications to aid in sleeping. I've tried the NyQuil approach, and I was way too groggy in the morning. Now, I just go to bed extra early, knowing that it's going to take me a long time to fall asleep. I like to wake up about three hours prior to the race (depending on the race obviously. Triathlons may require a little more time before the race). When I wake up, I have some sort of small breakfast...maybe a bagel and a banana, or maybe an Ensure (like an instant breakfast shake). I also get the coffee brewing and have a decent sized cup of coffee right when I wake up. Once all of that is done, I slowly sip on a small bottle of electrolyte drink. This is key, because you have to make sure you don't drink too much, otherwise you will be needing to visit the port-o-let quite often.
After all of this is done, it's time to head on down to the race and enjoy the day! Some other things that you can do to help settle the nerves is listen to some music, do some light stretching (and I do mean light! You don't want to pull a muscle before your race starts!!!!), or maybe even just head down to the race start to get excited for the race!
Whatever you do, it takes a little trial and error. Once you find something that works, try to replicate that each time you race, because it will help keep you calm and relaxed.