if it was as easy as looking up common questions and 'being yourself' then everyone would get in ¯\_(ツ)_/¯
not saying you can't practice on your own, but i disagree with the mentality that advisors or mock interviews are useless. it's an investment for your future like anything else, and a professional who is trained to know what works and give you objective feedback can be incredibly helpful.
You can and should still work on your own too, of course, do your research on the school you're interviewing at, know the answers to common questions and practice out loud, know your experiences thoroughly, work on your body language, etc.