When I first started trying to take care of ME first, I had to pretend that I was a separate person from myself. I would ask myself something like "Self, if you were an outsider, how would you treat the Other Self?"
Only by making me not be part of me could I change the habit of putting others' needs before my own.
I'm much much much better than I used to be about this, but I still fall back on this trick of stepping outside myself and asking how I would treat another person in my situation when I feel myself neglecting me.
Just a thought. Take what you need, leave the rest.