Don't dress like a tourist, don't act like a tourist, pay attention to your surroundings. Tourists are targets for crime because the criminals know that in order for them to face charges, the tourist has to show up to every court date. They will purposely delay the court as many times as possible in order to make the tourist give up, if the tourist even shows up at all.
Don't get drunk in public, you will be a prime target and easy prey if you do. Don't trust vendors to give you the correct change, use a currency converter on your phone and do the math yourself, that is one way that they target you.
Keep an eye on your stuff at all time, keep your wallet or valuables in your front pocket or inside coat zippered pocket. Never let go of your bags in public, even to help someone else. Thieves will work in teams, one to distract, one to rob your belongings.