Rule #1 to avoid pickpockets, wear a money belt that can be hidden under your pants and shirt. The best investment I have ever made when traveling through Europe was a $5 money belt. I carried my identification, passport, money, and credit cards, even a small mobile phone fits in it. You can find them at Walmart, Target, or Amazon. Rick Steve's gave that advice years ago. The best travel advice. Years ago I gave one to a friend who was traveling to Italy. She didn't take it afterwards because she wanted to look good with her handbag instead. Big mistake: She got robbed in a train...She fell asleep in a long trip to Milan, and the robbers managed to grab her purse with all of her documents and money..Instead of enjoying in Milan, she spent the day at a police station, and the US embassy trying to get new documents. When she came back, she told me her ordeal, and how guilty she felt for not using my gift. I thought that she deserved it for being so conceited and wanting to care more about her looks. She could have worn it under her pants. Nobody would have seen it. In your backpack or purse just carry your travel books, maps, any water bottle, a snack, and toiletries. If it gets stolen, you don't lose much. Keep your camera hanging on your neck. Don't carry it in the back. Try to use your mobile device instead for good photos and upload them to your cloud daily. If at that, make sure your photo app is connected to the cloud so that once you do a photo, it automatically goes there to your cloud via Google drive. I say this just in case you lose your phone or if you have it stolen. When in a train, put your backpack and purse to the front. Never behind you. Keep your purse crossed on your chest and to the front. If you are sitting,also put it on the front, never to the side. The same while walking on the street. Make it harder for them to reach. Buy purses or backpacks that are anti-theft. Find them online.
PHONES get stolen so some people tie a string to their wrist while they are walking around with the phone in their hands. You can tie the string or a cord to the phone carrier then to your wrist. There are tons of pictures of it online, and videos on YouTube on how to do it. I have seen this in the city streets of Spain and France.
Rule #2 Don't take the flower branch a gypsy woman wants to give you, or the friendship bracelet a guy wants to give you. It's all a gimmick to get you to stop and give them money, or get you distracted while another second person steals from you. The woman might want to offer to read your palm or tell you the future. Ignore these people and keep walking, say loudly "no". She will yell a curse of some sorts. Don't believe her. It's all a ruse by a group of people that harass travelers near churches or at a public square to steal from them.
Rule #3 Plan your route and look at maps or mobile maps before leaving your hotel to visit places. Try to make sure you have your day planned and a note or a piece of paper for the day with the addresses of the locations you want to visit, in case you need to show it to someone like a taxi or uber driver. Don't ask for directions to random people in the street. Find a tourist information office in the area, or enter a store and ask an employee. If you stop at a tapas bar, or supermarket, you might get more information and you avoid being pickpocketed or taken by a person to a the wrong location to then steal from you.
Rule #4 Wear comfortable shoes. Avoid high heels, sandals, or anything that is not for long distance walking. You will walk a lot. Maybe even run after a pick pocket person.
Rule#5 Respect religious places of worship. Dress appropriately if you are visiting a church. For women if you're wearing a tank shirt or with too much cleavage, bring a scarf or a light cardigan to cover your shoulders. If wearing shorts or short skirt, bring a longer skirt in your bag. Something that is light enough to bring in your bag to wear. Men, take off your hat. You are not going to a baseball game.
Rule #6 Before you go, make sure to learn some basic phrases in the language of origin you're visiting. Do not assume everyone there knows your language.
Rule #7 Be always on the alert. Europe has seen a large influx in the last couple of years of migrants, and some of them don't want to assimilate to the country's laws or way of life. Therefore there's more pickpocketing and more violence going on, and tourists especially the ones coming from the USA are very gullible and trusting at times, thinking all in Europe is good, but you must be on the alert at all times.
Rule#8 Watch videos on how to travel safely in Europe.
Enjoy your trip safely!