Get Better Equipment
You might be saying, wait a minute. Does better equipment equal better photos? Def NO! But it can make it much easier and more fun to shoot. Tilt screens on cameras are amazing if you want to vlog for example.
Use The Back Camera Of Your Smartphone
You often do not need to have a professional camera if you have a great camera on your smartphone. But one thing you should def be careful about is using your back cameras. Do not use the the front cameras, as it can distort and have significant less quality.
Preparation
We all like beautiful photos and nice aesthetics. One thing you should always keep in mind is that your fans are here for you, for you ONLY and not the microwave or dishwasher in the background :) Try to keep your setting clean and organised. Do not be messy.
The Right Posing
A Video says more than a thousand words... Check this one
https://www.youtube.com/watch?v=ff7nltdBCHs.
Edit - Not Too Much!
It is so easy nowadays to edit images, remove pimples and improve skin texture. BUT it is also very easy to do TOO MUCH! Be careful that you do not look like a plastic doll, most fans like authenticity and want to see the real you.
Be Confident
If you ain't confortable, don't post it. Practice, practice, practice. The less you have to worry about lighting, camera settings, the more you can concentrate on yourself, being natural and confident.