-Research ahead of time. Learn about the culture, the people, the standards of behavior and beliefs. Study the city(s) you'll be in and get a feel for the geography of the place. Learn the major routes between your destinations in the city so you'll be able to tell if a driver is taking you off course. Determine back-up routes just in case, including using public transit.

-Make sure that multiple people know your itinerary in detail, and check in by phone or in person with the US Embassy/Consulate in country so they can contact you/track you if necessary.

-Keep contact info for in-country and out-of-country POCs handy.

-Memorize (or at least have handy) common phrases and basic questions in the local language(s).

-Some people will advise you to avoid revealing that you're an American. I don't agree, though flauting it is always bad. Disregard if you're not from the US.

-Travel in groups and avoid spontaneous side trips.

-Wallet in the front pocket, and don't carry large sums of money on you. If you're in a reputable hotel, use the hotel safe to store a spare credit card and a photocopy of your passport/visa. As you said, don't wear a lot of expensive jewelry.

-Dress to fit in. The more you blend, the better off you'll be.

-Respect local customs, particularly in terms of attire, manners, and diet. I can't emphasize this enough.

-Don't get drunk. Period. Not even in your hotel room late on the last night in-country.

-Always have a backup plan if a flight is cancelled, train breaks down, or whatever. Also remember that discretion is the better part of valour. When in doubt, withdraw to a safe location and consider the situation for as long as it takes.

-Remember that you can't plan for everything, and that being paranoid annoys people. Be smart, be safe, and then just relax as much as you can. Few places are bad enough to put you in a lot of danger, unless you're personally a target for some reason.