Don't take selfies in low lightning. Darker photos get a lot of noise.
Don't frame the face too large. One third of the image area is maximum, slightly tilted face and positioned in the top-center.
Don't take group selfies. Group shots are never good photos of an individual, always be the only person in the image.
Filters are good but not essential. Black and White does well, but anything that decreases the contrast works.
Women get consistently more reactions than men. That is just the way it is.
If you have long hair, show it. Long hair always receives more likes; men or female.
Show your shoulders if you are male. The broader the shoulders, the better.
- some machine learning experiment I forgot