Never share pictures with your face on it, especially combined with (semi) nude body parts. These could be used for extortion/blackmailing.
No recognizable objects
Make sure nothing on the picture could be useful to figure out your location, or other details about your real life. Even a small thing like your company's pencil could give away more than you want.
Do not re-use social media pictures
People can try to reverse-search your pictures, and if you have posted them before on your social media, you could be tracked down.