perchlorate - ClO41-
chlorate - ClO31-
chlorite - ClO21-
hypochlorite - ClO11-
If you look at the chemical formula and charge of the polyatomics, the only difference between them are the number of oxygen (the charge remains the same).
per - stem of word - ate { 1 more than -ate (highest number of oxygen) }
stem of word - ate { one higher than -ite (this is one I memorize and link to rest.) }
stem of word - ite { one less than -ate }
hypo - stem of word - ite { one less than -ite (lowest number of oxygen) }