Oh, no, not redox again....
OILRIG – oxidation is loss, reduction is gain
Elements – oxidation state is always 0
Compounds always 0, BUT
Compound ions and any other ions add up to their formal charge.
O-2 (except with F)
Halogens-1 (except with F or O)
H+1 (but -1 in metal hydrides)
Remember this is a hierarchy, top rules rule and if you need to know ones that aren’t here, it’s based on electronegativity.