What does it take to have a great RC car race? I give you one word – practice. Of course, there are other factors (such as equipment, overall set up) which contribute to a racer's victory or loss but it all boils down to a good practice run.
Go ahead and check other reading materials focused on RC related topics. You've realized that practice does make a difference to how your RC car performs during the actual competition.
When you get to the venue, you can start practicing (that is if you have already signed up for the registration) on the track. Do not get too excited though, your first practice run should be all about getting the feeling of the track, familiarizing it which means there's no need to go running on top speed just yet. Learn how the track is laid out and master it if you can. Also, during this time, use an old and worn battery pack since running the track for the first time is not going to be pleasant at all.
On your next run, focus on your car and how you can best handle it. During your second run, try to see or feel anything that you think is not going to work out for you on the actual race. If everything seems to work okay do not change any of your settings. After completing this run, you're ready to go on your last and final run for practice. This time though, you need to shift your focus from all the other elements on the track to just your car and nothing else.
You have to realize that by this time, you can make any last adjustments you desire but then, do not attempt in doing so if you're not comfortable with it. To make sure that your settings is going to work accordingly, try to setup your car to the nearest setup ideal for the track. Although you may not set it up accurately, (since there's no such thing as perfect) you're at least getting it working efficiently on the track during the race.