Next time you take a picture of something, rather than just pulling out your phone and taking a picture of it from where you see it, take your time with it. By take your time, I mean if you have 2 minutes to change one thing, take the 2 minutes; if you have an hour, you can change everything.
Say you have two minutes, and you can change one thing: then change the light. Photography has to take a three dimensional object and compress it into a two dimensional image. Better photographs tell us more about the object through better lighting.
Here’s the trick: for better pictures, you don’t want brighter lights, you want bigger lights. Find the biggest window in your house, ideally south facing, and stand so one side of your face is nearer to the window than the other. Try changing the angle a bit to change the shadows on one side of your face, to give a gentle shadowy look. Try and keep the background as simple as possible and bang, better selfies straight away.