If you're a US citizen, enroll in the Smart Traveler Enrollment Program (STEP). This program allows the US government to notify you regarding potential security threats.
Travel insurance has multiple benefits. Not only will it help you out in case you get hurt, but it is also great if one of your belongings are stolen
If you get lost, your phone dies etc. it is good to know the address of the place you are staying in your mother tongue and in Spanish
Keep a paper copy with you at all times and leave your original in the hotel safe.
Type out a copy of the hotels you plan to visit by day and give it to a trusted person at home.
It’s easy to get distracted by all the beautiful new sites, but you need to be aware of the people around you. Look around often and avoid standing in large crowds.
It’s best not to carry much money at all, but if you have to, divide it up. I put some in my shoe, some in my bra, and some in each of my pockets.