Where do you only use shampoo when washing your hair?

I'm upset because my hair has gotten thinner than before and the crown of my head looks sparse.

I heard that how you shampoo helps with hair loss management.

I usually start by rubbing shampoo into my scalp. Since my hair is long, I try to shampoo my whole body, so I think that's why I ended up starting with the scalp. Some people say not to shampoo the scalp, so what is the best method?