Honestly, for me it was getting to know myself.
Relying on other people's validation is one thing, but coming comfortable with yourself and accepting who you are is another ball game entirely!
I basically began by trying new clothing styles. I always wore black and was just generally not comfortable or confident enough to wear anything else. On a good day I would take a mirror picture of myself because I felt I looked GOOD.
I never posted anything or asked anybody else but as I experimented and just generally started on the journey to find out what I loved, I began to love myself.
I can't give any professional advice, or provide you with something that is a single fix for everybody, but this was something that worked wonders for me.
Experiment and learn what you love about yourself.