Be aware of your surroundings at all times.

There is always something going on. When you aren't familiar with the area you are in, you could end up getting hurt.

Watch your belongings.

When you are traveling in a place that you are unfamiliar with, especially in crowded spaces, watch your belongings. If possible, make sure they are in front of you at all times. I learned this one the hard way when I was pick-pocketed.

Respect the space around you.

If you are a visitor at any monument or historical area, respect what is around you. If there is an area that is roped off, it means don't go there. Don't just throw your trash anywhere you please. If you are in a chapel or any historical place of worship, be respectful and don't talk. Put your phone on silent. Some people go there to pray and have to be interrupted by noise. Don't let your toddler stand on the ledge of the Colosseum.

And possibly the most important of all, if you are taking pictures somewhere, be mindful of if the pose you make is appropriate for the situation and setting you are in.

Don't make eye contact with street vendors.

If you don't want people coming up to you trying to force you to buy their product, do not look at them. The street vendors are more likely to keep pressuring you if they notice you are paying attention to them.

Do not be afraid to just walk away.

This is one thing that I found the hardest. When someone that is selling something on the street at any major tourist attraction, they are presistent. They start an interaction with you, and they are fully prepared to continue it until they have your money in their hands. If they hand something to you and don't let you give it back, do not be afraid to just set it on the ground and walk away.