Léon is a small, and somewhat ugly city, and therefore not much of a tourist attraction, so most of the tourist-fraud schemes won't be common there. I have spent many months there, and will be visiting again the end of next week.
I don't know your nationality, or how you'll be arriving (by air, bus, driving), so I can only offer a few general suggestions. Most of these tips apply to any person, in any foreign city.
León is not a particularly dangerous city, but of course there are neighborhoods you should avoid alone at night, same as in any city. Just use common sense, don't walk down dark alleys.
People in León are generally friendly and helpful, as they are in most parts of Mexico. If you speak Spanish you will have no trouble... if you speak only English, you'll almost certainly find a few people who can help you if you get lost or need help finding a restaurant, or whatever.
Don't leave valuables unattended--even in a locked vehicle. I had my laptop and many other things stolen out of my trunk while I was in the supermarket in León for only 20 minutes.
Don't act like a tourist. I'm a 6'2" American man. I stand out like a sore thumb in León (as in most parts of Mexico), but I walk with confidence, as if I know where I'm going (I usually do--but even when I don't, I pretend). Do the same, and you won't be as much of a target. Especially in places where tourists abound (bus station, airport, etc). This includes not walking around with expensive clothing, purses, or cameras around your neck.
If you take a taxi, either negotiate a price before getting into the cab, or ask to use a taxi meter (and the taxi meter is probably the better bet until you know appropriate prices). Otherwise the taxi driver will probably gouge you.
Be friendly, and don't appear to be frightened. An attacker/thief is less likely to attack you if you appear confident. Look people in the eye, and smile, and say "Buenos días," "buenas tardes," or "buenas noches" (depending on the time of day), and most people will return the smile and the greeting. And if they were a potential attacker/thief, they probably aren't any more, once you've built a small bit of rapport. In Mexico, it's appropriate to greet strangers with a smile and a hello -- although there are places where this might be considered overly friendly, or even be perceived as sexual advance (especially when done to the opposite gender), this isn't a concern in Mexico.
In short, there's nothing special or unique about León that you wouldn't likely encounter in most cities, even in the US (aside from the language difference). The main exception is that the police won't take robbery reports seriously, and the police may even be colluding with the thieves. So just be extra careful not to expose yourself to unnecessary risk of theft, since you'll probably be on your own with no recourse if it happens.
And finally, as an aside, if your schedule permits, take a small detour to the city of Guanajuato, about 45 minutes southeast of León. It's probably the most beautiful city in Mexico, and well worth the short drive, if you can swing it! You'll want at least 2-4 hours to see the downtown area, although you can spend 2 weeks there and not get bored, too.
