Not sure if this has been said or not, but here is a very simple *yet very helpful* tip:
Playing against humans is way different than playing against AI.
I will take my Garou experience for example. I can hold my own against humans in Garou reall well, but I can't even beat stage 4 in arcade mode anymore.
If you want to play against humans, do not play against AI. It will teach you very bad habits that will get you punished later on, and vice versa.