So is the goal just to completely max out a skill tree? I mean is there anything not worth taking. I have a Gold Harley Quinn Cerebella and I want to build her right so I am asking what other people did.
Yes, the goal is to fill out the entire skill tree. However, if you're just starting to work on it, the first thing you should do is get the extended combo and the character skills. Working on atk and hp during or after this also helps to get the fighter in decent shape, but you're gimping yourself early if you don't have a full combo.