Some reassuring news for your trip to Argentina: Argentina is considered to be the safest country in Latin America. Please note that this does not mean that danger does not exist at all. You must always remember to remain vigilant.
The European ancestry of the Argentinian population means you should be able pass somewhat unnoticed in a crowd and thus avoid a lot of the main risks on your trip to Argentina. Tourists are, in fact, the favourite target of pickpockets. There's less of a wealth gap between the citizens of Argentina and tourists than in other countries on the continent. This is one of the reasons why delinquency is less visible and less commonplace. This doesn't mean that the risk of being robbed or facing violence is totally non-existent. However, you'll generally feel safe in Argentina.
Some places in Buenos Aires are sort of dodgy. Which could be said of all world capitals. Even if things seem safe, that's no reason to be overly trusting and get mixed up with the drug dealers that hang around some neighbourhoods. As exciting as it may seem, the danger is real and the consequences can prove to be extremely serious. You should also note that if you get charged with drug possession, you face up to 12 years in prison.
In Buenos Aires, a lot of the bank notes exchanged on the streets are counterfeit. This is especially prevalent among 50 and 100 Argentine peso notes.
To avoid being a victim of pickpockets, be vigilant and always keep an eye on your things. These petty thieves usually frequent public transportation. In order to avoid attracting attention, travel in a group and try not to look too "tourist-y".
If you go for a walk in La Boca, the most beautiful and historic part of Buenos Aires, stick to the roads that are popular with tourists. Outside of these streets, the risk of getting robbed or attacked is a reality. If that should ever happen to you, above all else, do not resist. Stay as calm as possible and give them what they ask for. It would be wise to keep a certain amount of money within easy reach in case you are robbed. It's not a matter of "just giving up", but if you do so, your attacker is more likely to just take that money and leave you alone.
One last thing: never change money in the streets or anywhere outside of a bank. Counterfeit money is commonplace in the Argentinian capital.