1) if you can afford it, take a burner phone w you; leave main phone at home.
This will ensure your info is safe on the main phone, & if anyone tries to geotrack, your main phone isn't present there.
This also protects your phone from being confiscated in case arrests happen.
2. Only save emergency contacts in your (potentially burner) phone who you can immediately inform in case arrests or violence erupt. Also a good idea to write these numbers somewhere on your arm or inside of your shirt where they can't be seen or erased.
3. Don't record content directly from the camera. Instead put phone on airplane mode, open camera & then record screen. This will help reduce the amount of metadata linked to your photo. For remaining metadata, use an exif cleaner before uploading photo/video online.
5. When you do upload content after the protest, blur visible faces and any other identifiable features in the photos/video. People's faces, clothes, tattoos, scars, marks etc. You can use blurring tools or draw over faces within your gallery.
Respect others' privacy & safety.
6. Encrypt your phone + sign out of all your accounts and remove saved passwords before going to the protest, so if your phone gets stolen or lost, your data is safe.
7. Wear clothes that you don't want to be seen wearing again. Cover any tattoos & scars. So in case someone tries to identify people afterwards, they can't identify you. Consider wearing clothes with no prints or patterns. And of course, wear a mask.