Bolivia is the safest country in Latin America. This does not mean the country is crime free.
There is a (well-founded) belief in this country that white foreigners, "gringos," carry a lot of money. However, if you take due care, the possibility of being the victim of crime is very low.
One of the most common problems is the "express kidnapping." A new system adopted by criminals is to pose a taxi drivers and operate in the richest areas of La Paz (the south and Sopocachi) in cooperation with two or more criminals who hold and torture their victim, forcing him/her to withdraw money from an automatic teller. To prevent this type of incident, it is recommended that you call for a taxi you know (hotel taxi or recommended by a friend).
Another type of common attack by these evildoers is to pose as police and request documents. It is very unlikely in Bolivia that a police officer that is not in uniform would have the right to ask for your papers; however, many times they use a disguise (identical to a uniform). In both cases it is recommended that you ignore it and leave since even the police do not have the right to pester foreigners..
When walking along the street, stopping to eat and/or drink (in a restaurant, coffee shop, bar or discotheque) or on a bus, keep an eye on your personal effects, since there is always someone around to take advantage of inattention.
If you want to change money, it is better to do so at an exchange center (casa de cambio) or bank since counterfeit money is quite common.
Cochabamba and Santa Cruz are the most dangerous cities in Bolivia since they are in areas of drug trafficking where there is a greater tendency for organized crime.
If you keep these recommendations in mind, the only risk is that "you may want to stay," like they say in the Colombian tourism advertisements. Don't forget, Bolivia is the country with the lowest crime rate in Latin America.