Wear a fanny pack for valuables instead of strap purses or back pocket wallets which are easy to steal.  Try not to carry large quantities of cash on your person, and never show large bills or count money in public areas.  Purchase a money belt or other hidden security pocket for under your cloths.  Most luggage stores sell them.

When traveling with a spouse or companion, have one person carry one brand of credit card (Visa) and the other carry a different brand (M/C).  If one person looses their wallet only one card has to be cancelled, giving use of the other one.  This also works good with two ATM debit cards if they are drawing cash from different bank accounts.  Leave extra credit cards at home.

Take minimal jewelry with you.  Flashy expensive jewelry makes you a target for theft.

Keep a low profile: Do not wear bright extravagant cloths that make you stand out.  Try to blend in with the locals as much as you can.

For personal safety when on outings, make sure all persons traveling with you know the importance of being back punctually at agreed upon times.  Always know where your friends and relatives are!  Report to local police promptly if persons are overdue from outings.

Avoid daring bathing suits that might draw unwanted attention.  While accepted in resort areas, they are unsuitable in smaller rural coastal towns.  You could be attacked or arrested.  Bathing suits and immodest or outlandish clothing are inappropriate for shopping and sightseeing.  You would show lack of respect for Mexican customs and culture.

Never carry all your forms of ID in the same place; split them up in case of loss or theft.  Record your credit card and passport numbers and store them separate from credit cards.

Do not carry large bladed knives or other items which could be mistaken for weapons.  This could cause you serious problems with Mexican customs and/or local police.

If bringing travelers checks, swap the registry of check numbers with your traveling companion.  If your checks go missing you will have your numbers when you phone for replacement checks.

Try not to walk alone or drive a car at night or in remote areas.  Take a small toy plastic whistle to draw attention if you are in personal danger.  Only take rides from taxis that are stationed at taxi stands.  Catching one on the go could prove to be unsafe, especially in large cities.

Take these important phone numbers with you to call in an emergency.