As a blogger, what should my first blog post be about?

Definitely an introduction of yourself, your interests, and the main theme of that blog. That will serve as a foundation for the succeeding topics you want to write. 

It's up to you. Write according to your desire, not on the dictates of other people.

Write about yourself , and what you believe in or what you love

Thank you for your good question

That depends on what you would like to be known for. Would you like to be known for particular content with a particular theme? Start with that theme you would like to be remembered with.

i think you should firstly post about yourself.