Okay, since we ran into a little problem already with a certain breakfast food, I've got two things to say.
1) Do not leave your city running unattended, if something goes wrong while you're not there its effects can bleed out to the other cities in the region. (Protip: Disasters can be disabled in the settings under Gameplay)
2) NO FUCKING VU TOWER GOD DAMNIT. If your police force sucks ass and you have things causing crime it fucks up everyone else's city. I'm a tiny town and I have an entire full jail of criminals in a day.
Bottom like, keep your city running well. What you do affects the region, so don't make your city a pile of shit because it stinks up the whole place.