While Puerto Vallarta is generally very safe and hospitable, as with any large city, it is a good idea to take precautions and be aware of your surroundings.
Puerto Vallarta has many branches of police and public protection, as well as having tourist police who speak English. Dressed in white uniforms, they are usually stationed in the more touristy areas of the city. More often than not, their assistance is for nothing more than giving directions and answering questions.
Don't carry around large amounts of money, not necessarily for theft, but also loss or misplaced purses in taxis or wallets that slip out of shorts pockets. Most hotels have in-room safes or deposit boxes.
Don't wear expensive jewelry. Once again, not a precursor to impending theft, but strong advice as many people misplace jewelry at the pool, or a ring can go down a sink drain. If you don't want to lose it, leave it at home.
Make photocopies of your credit cards, traveler's checks, passport, airline tickets, or birth certificate and license. In case these items are lost or stolen, you have the information you need right at your finger tips.
Who are you? Make sure you label your suitcase with not only your home address, but with hotel or accommodation you will be staying in. It is also a good idea to tuck into your wallet or purse your name and accommodations in Puerto Vallarta. You should also label your camera or camera case. Many taxi drivers, waiters, and others have spent countless hours trying to locate owners of lost or misplaced items.
Drink with a buddy. If you plan on imbibing more than the normal share of alcohol in a normal evening, make sure you are with someone you trust. Keep a clear head and be aware of your surroundings. Someone who is obviously intoxicated is a blinking target.
Drugs. Drugs are illegal, period. Nothing will ruin a vacation faster than Mexican jail.