I think my suggestions pertain to safety:
If taking local transportation (non-tourist class), do not keep valuables in visible view - i.e... Do not keep your camera around your neck; keep your money belt underneath clothes (not above). Be careful with your ipod or any electronics, as if you fall asleep with them on - they might be snatched before you wake up. This is a vacation so avoid electronics as radios and other unnecessary items.
Don't leave valuables around in your hotel room, Try to have a backpack with lockable zippers (vs. a drawstring top loading backpack).
Avoid being trying to get off the beaten track too much (though this depends how confident you are and what you really want to see. I am sure this statement will be contradicted by many). It has been known that people in La Paz attempting to get a better view of the city wandered out into the outlying areas and were mugged.
Try to keep your money spread around (keep some in your shoe, etc) so that if you are mugged, it is not a big deal.
Avoid carrying a wallet around with your cards. I found that keeping a small change purse with less than $20 in it was helpful. If you do get mugged, you can give them that and not be that worse off.
Walk with confidence and keep your eyes straightforward rather than nervously looking around. If you look uncertain, you are an easy target for vendors and other people who want your attention.
Keep photocopies of your passport and other important documents online and on you so that if things are stolen, it is easier to get a new passport.
It might be easier if you keep a smaller backpack that will be allowed onto the bus rather than stored below or above. If it is too big, you have to check it and it is hard to keep an eye on it especially when the bus stops every five minutes and people get on and off.
It looks dorky, but keep your backpack in front of you (wearing the straps on the front) especially in crowds so that you can tell if someone is trying to get into your bag).
Carry small key rings, safety pins, or mini-com locks to lock up your day-bag. While this will not prevent a professional thief, this does deter a petty thief who is trying to get into your bag without you noticing.
Bag slashing is something that I have heard about (but never happened to my friends or me). Always carry a shoulder bag that has sturdier straps (so it is not as easy to slash) and never carry anything valuable in it that could be emptied if your bag was slashed. By slashing, your bag straps can be cut so that your bag falls off you or bag slashing can mean that they will slash the bottom of the bag/backpack so your contents fall to the ground.
I have never been mugged but I have heard plenty of stories.
Bottom line: Do not bring anything that you would be incredibly sad if it was stolen (this even pertains to a watch or jeweler). Things that we carry around (that we take for granted) can easily equal a farmer's half-year salary.
If you were still worried about specific violence or dangers, I would recommend checking out your government's travel advisory. For another perspective, I would recommend checking out Canada's government website and scroll down for the specific country. They are good for letting you know about specific places and warnings pertaining to it:
You can also find important tips at this website, http://www.katharinaandpeter.info/
Some of my advice for South American cities:
-- Always, appear to know where you are going. Do not walk around showing your map or guidebook in any big cities. If you need to check a map, walk into a storefront.
-- be very careful with people who appear to be cops. Do not let them force you into an unmarked car. This has happened at some La Paz bus stations (as well as elsewhere).
-- try to be especially careful near notorious border crossings. It is very helpful to take a bus service that helps with border formalities. Otherwise, you risk being dropped off in a scummy border town and having fraud artists prey on your confusion. the main Ecuador Peru border crossing is an example of a bad border for backpackers--I've heard of countless taxi scams there (you get in a taxi to go to the border post and they drop you off in some remote walled-compound with people with guns and clubs and demand all of your money so they can protect you)
-- be careful walking around alone at night in some cities.
-- On long bus rides, always carry plenty of food, water, and warm clothes (if necessary)
I have had no trouble in remote parts. In my opinion, the cities (or anywhere tourists especially congregate) are where you should be cautious.
I just wanted to add a general warning from my 7 years of experience.
Use this key warning: DON'T TRUST ANYONE I know it is a bit harsh but I think this rule will keep you safe everywhere in South America. What I mean is that you need to use common sense. If you do not feel comfortable with the information, you receive, just leave, or find other sources. Try to go inside some place when looking for information.
Under this rule:
1. Don't show off- meaning wear simple cloths preferably light cloths. Do not bring expensive cloth, jackets, or snickers. Do not carry with you ANY expensive electronics (ipod camera watch etc.) especially by night unless you are in a group. Bags attract too much attention- carry your staff to the beach (or for travel around the city) in a plastic bag or small simple bag.
2. Don't carry money/credit cards/traveler checks on you everywhere you go. Take only enough money for you to spend in one day (30 Euro is enough).
Do not use traveler checks, the commission on cashing them is excessively high, and the places to cash them are very few. Take a credit card -you can find many ATM's almost everywhere
Use the HSBC ATM's they give the best rates at least in Brazil (use the ones inside the Banks because they will not charge you extra commission and they are safer). Do not forget that outside criminals can use a system to retain your card when used at the teller machine or can suddenly also assist you with withdrawing your own money. Check always around the area of the bank or teller machine for your own safety.
3. Don't walk on your own. Walk always with someone. If you are being robbed do not argue, do not try to run away, just give them everything they want, the robbers get violent very easily. It does not worth getting hurt for some money.
4. be very careful from the police officers especially in Rio. There are many corrupt police officers in Brazil and they have the tendency to plant drugs while searching (usually near clubbing zones). Keep your eyes open while you are being searched and this is another good reason for not carrying too much staff with you. DO NOT TRY TO BRIBE THE POLICEMAN.
5. At the beach do not let anyone to watch your staff (if you care for it) unless you leave them with someone, you trust (another tourist). At the summer there are many teenagers gangs that wash the beach running from one side to the other, grabbing everything visible and valuable (mostly handbags and cameras), if you see people start running, grab your things and run away. They can be violent too. It is called in Portuguese RASTAO so if you hear people on the beach screaming this word, start running. People have seen this in Rio and in Salvador de Bahia. I'll say it again DON'T CARRY VALUABLE STAFF WITH YOU learn from the Brazilians, they go to the beach only with swimming suit and plastic bag with tanning cream and towel and small money. If you wish to take pictures do it in one day together with your friends so you will not need to carry your cam with you everywhere.
6. Beware from all the salesmen at the beach, some of then have the tendency to take your belongings while showing you their merchandise, they work in two or more.
I know that all these warnings might scare you so I want to say that you should not be. You can enjoy your vacation a lot if you will be careful. All countries are amazing especially in South America and the people are very friendly, it is the poverty that makes some of them violent. If you will take the right precautions and try to behave like them, the worse thing that may happened is that you will lose some small amount of money. It was always small money or simple cell phone. By the way, a cell phone is very necessary. You never know you might need to use it. In addition, always avoid traveling alone. There are always dangerous areas e.g. some streets in la Boca, Argentina but ask around for local knowledge.
Do not forget that where most travelers come from (North America, Europe, etc.) crime is also a problem.