Start with research. Find out everything about a country before visiting. Read blogs, ask questions on prominent forums, and join Facebook travel groups. single female travelers should question other single female travelers about their country experiences.
Start small when first solo traveling to ease into it. Before traveling solo abroad, I visited adjacent cities and states. I had already been abroad in groups (EF College Break & Study Abroad), so I knew I wouldn't experience culture shock.
I meet numerous folks who say they don't see their surroundings when walking. You may wish to adjust that when traveling alone. Watch the people around you, close and far. This alerts possible predators and helps you catch them.
If your passport is lost or stolen, print copies to carry. Keep a copy on Google Drive or Dropbox for easy access from any computer in case of loss or theft. Email your parents/loved ones a copy to send you if all else fails.
Protect your passport by locking it in a secure location and only carrying it when needed. Buy a TSA-approved lock to protect your belongings when traveling. It's unnecessary to take it to the beach or nightclub!
Just for safety, not Instagram or Facebook. If you're bad at directions, Google Maps may make you feel safer. Wandering and being lost are different. Look lost to be targeted.
It may be comforting to phone or text family if needed. Luckily, T-mobile offers free international messaging and data. Once in the city, you may want to buy an international plan, data hotspot, or SIM card if you don't have T-mobile.