Eventually, you will learn how to pace yourself during a race. You will develop a sense for what a given pace feels like. But until you do, one tool you can use to help you during a race is to know about where you should be finishing. You can do this in big races because you can probably find results from the past year's event.
Here's an example.... Our team is headed to our first invitational of the season this weekend. The newer runners ran their first official race of the season last Friday on a course that is about the same length. Using their per-mile pace as a guide, I could estimate what their time might be this coming Saturday. Based on that time, I am able to guess about where they might finish. For the fastest guys, they will probably be in the top 20 (out of 150-180 runners). The medium guys will probably be in the top 50 or 60. So I can tell the fastest guys that if it looks like there are a number of guys about equal to the total number of guys on our whole team (about 30) ahead of them, then they are probably going too slow. Similarly, if the medium guys see only a couple dozen guys ahead of them, they're probably going out too fast. For the slowest guys, it's probably best to primarily use their own teammates as a guide, i.e., they shouldn't be keeping up with guys they know will finish a minute ahead of them.
It's also possible that you might look up previous years' results and find that you might actually have a chance to win. The only downside of this knowledge is that you probably shouldn't get out and try to lead wire to wire - you might accidentally start out too fast. Instead, you should be a little more patient, and let someone else lead for the first half of the race or so, then move ahead after you determine that's the best plan.