Basic rule of thumb is that hanging is for business clothes, fancy clothes, blazers/jackets and thing you don't want wrinkled. But if you have a larger closet, I suggest hanging as much as you can. Don’t hang sweaters or heavy knit fabric because it can pull and cause the clothes to be mis-shaped.
Everyday pants can go either way depending on space. Items that go into drawers should be file folded. It is simple and makes it easier to find things. It also looks so much nicer than stacks.