First and foremost, your belongings are only as secure as you are willing to keep them. If you are careless, or don't follow all the reasonable steps you should, a certain amount of risk creeps in. Nothing you can do will 100% guarantee any item is secure. Keep this in mind when packing for the trip. Consider whether you can afford to lose any item you pack, both financially and emotionally. Think about what can easily be bought at your destination so that you can leave more behind. Before you leave, look into an appropriate amount of insurance. If you are traveling to a foreign country, especially one that is known for pickpockets and theft, get as much insurance as you can afford. It is worth the relief when something goes wrong. Make several copies of anything that has information on it, like a passport or a vaccination certificate. Leave a copy at home and distribute several copies amongst your luggage.
During your travels you need to constantly be aware of yourself and your possessions. Don't let your bags go out of sight unless it is absolutely unavoidable. Try and minimize the time you spend physically carrying your luggage around with you. If you are encumbered with a heavy suitcase, you are less likely to give pursuit if someone snatches your wallet or purse, so make sure these items are very close to you and, if possible, hidden out of sight. Make sure you always check any seats you have used for anything you may have dropped or forgotten. Though this advice sounds obvious, maintaining an automatic awareness of your personal security is something that has to be practiced over time until it becomes almost subconscious.
You are at your most vulnerable when out in crowded places. Sizeable amounts of money, passports, or any other valuables should be kept underneath your clothing in a money belt or some other zippered pouch that isn't your main pocket. Any money you think you'll need during the day should be kept in a separate front pocket. You can top this up in private places to hide your money belt from view. If you are going to be carrying any bags with you, try and 'slashproof' them by running wire or mesh through the places that would likely be cut. Additionally, the less you show off in public the less likely you are to be a target, so keep electronics, expensive-looking bags, and bulky items hidden as much as possible. Consider getting a scuffed-up rucksack specifically for city travel. Remember, anything that makes you stand out as a tourist marks you as a target for thieves.
Practice these steps in the weeks leading up to your trip so that they become more automatic. As always, good preparation and good advice are the cornerstones to any enjoyable travel experience. There are many more extensive guides on security and safety abroad on the web, and more information can be obtained from the tourist board of your destination.
