Having a criminal record can put you in a bad situation in a lot of ways. Obviously, it can prevent you from getting or keeping certain jobs (including the military). But one thing that I think people don't often think of is that having a criminal record is that it makes you more likely to get arrested again (and, therefore, more likely to get a longer criminal record.)
Once in a while, I'll have kid clients who tell me, "I don't want to come back to court, I don't care if you're going to try to work out a deal, I just want to cop out today." Obviously, they're not thinking long term. I tell these kids, "If you cop out today, and get a criminal record because you're just too lazy to come back to court, then every single time, for the rest of your life, that you and your friends are out smoking a joint, a cop is going to come up on you, and let all of your friends go with a ticket or a warning, and put you through the system because you're the one with a record. Same with drinking in public, same with ticket scalping, same with just about any little crime you can imagine."
But, here's another problem. I have some clients who truly should have a clear record, but who don't because of a mistake on their rap sheet. I look through their rap sheet and say, "Ok, it looks like you had an armed robbery case last year, what happened with that?" My client says, "Oh, it got dismissed." I don't know whether or not to believe them because a lot of my clients think "pled guilty but didn't go to jail" is the same as "dismissed." But, occasionally, I'll run a check in the computers or speak to their lawyer and find out that their case was, indeed, dismissed.
A mistake on a rap sheet can make your record look much, much worse than it should. I remember hearing about a guy who had one previous arrest for a misdemeanor. Some court clerk must have put the wrong number in a computer or on a form, and the man ended up with a murder conviction on his rap sheet. It was obvious that it was a mistake if you took the time to look at it - the sentence was community service - but he might not be lucky enough to have someone who is going to look at his rap sheet carefully before questions him or detaining him on a murder, or setting bail on a petty case.
What can you do about it? If you have ever, and I mean EVER been arrested anywhere, at least do a google search for the name of the state and "rap sheet," "criminal record" or "expunge." Every state has some mechanism to get a copy of your rap sheet (you may have to pay a few dollars in administrative fees). The process will vary from state to state (in some states you may need to mail in a request, in others you may need to go somewhere in person), but it's always worth it to see what is on it. Get it and check that it really says what you think it says. If your case was dismissed, it should say dismissed. If a case was supposed to be sealed, it shouldn't show up at all.
If you can't figure out the process, try giving a call to a local public defender's office in the area where you were arrested, or the law schools in the area. They may have a "How to Clean Your Rap Sheet" pamphlet they can send you, or a paralegal, law student or intern who can walk you through the process. (I know we did a few of these in my law school's criminal defense clinic.)
Finally, even if you were actually convicted of a crime, and therefore, no surprise, you know you'll have a criminal conviction on your record, you should look into whether or not the state has an expungement process. In some states, for example, if you've only had one criminal conviction, and it was for some particular types of crimes (misdemeanors, for instance), you can have it cleared from your rap sheet if you go a certain amount of time (five or ten years, for instance) without another arrest.
Reentry.net is one great link I found with information on how to get and clear your rap sheet in many different states. If the state you're looking for isn't listed there, play around on Google, because I think that there are a lot more out there.
Now, go give yourself a clean slate.