The oxidation number of an atom in its elemental form is 0
The oxidation number of a monatomic ion is equal to its charge
The sum of oxidation numbers in a neutral compound is 0
The sum of oxidation numbers in a polyatomic ion equals the ion charge
Group 1 metals are usually +1
Group 2 metals are usually +2
Fluorine is always -1
Oxygen is usually -2
Hydrogen is usually +1
In metal hydrides, hydrogen is -1
Halogens are usually -1 unless combined with oxygen or a more electronegative halogen
Assign known oxidation numbers first
Use the total charge to solve for the unknown oxidation number
Check that the final oxidation numbers add up correctly