Good art is also very subjective, someone's good could be someone's fantastic or 'mediocre' but even so, if you truly want to become good at art, put your time into it and keep drawing it.

I know a lot of people will say 'but I've drawn for [x]' and I understand the frustration, I know I can do better but all in due time. Don't rush yourself, take the time to figure out stuff, look into getting criticique on matters you feel you struggle on. I.E I feel I struggle with anatomy or avian feet so I go to for general help there and the critique has helped me tremendously. I encourage getting critique on your work when you feel ready for it, it can help you in the long run.

DISCLAIMER TO ALL CRITIQUE GIVERS: Saying 'this looks bad' and not providing a way to improve it, does not work as constructive critique and just generally caling the piece BAD counts as destructive. Help the artist grow, don't slam em into the ground.