Rules for Assigning Oxidation States
If two rules are in conflict, the earlier rule is followed.

 1. The sum of the oxidation states of all of the atoms must be equal to the net charge on the molecule (zero net charge) or ion.
2. Oxidation states for all atoms in a pure element are the same.
    Oxidation states for all atoms of one type are the same in a binary compound.
3. Alkaline earth metals (column 2) are +2 in all of their compounds.
4. Alkali metals and H (column 1) are always +1, unless in a binary compound with an element which is less electronegative.
5. Fluorine is always -1. Other halogens are -1 except in their compounds with halogens or oxygen.
6. Oxygen is -2 except in peroxides and superoxides, usually with elements in columns 1 & 2.
7. In binary compounds, the element with greater electronegativity is given a negative oxidation state.
 

Oxidation: a loss of electrons - increase in oxidation state - e's on right.
Reduction: a gain of electrons - decrease in oxidation state - e's on left.

The reducing agent gets oxidized - the oxidizing agent gets reduced.
 Balancing Oxidation - Reduction Reactions:

You can't change the ions or compounds involved in the reaction. You can separate ionic compounds, but they must be restored in the final balanced reaction.

If water or any aqueous species are involved in the reaction, you may add water, hydrogen ions, or hydroxide ions to balance the reaction.

You can't have hydroxide ions in acid solution or hydrogen ions in basic solution.

Inspect the Reaction that is Given:
1 Determine what is being oxidized and what is being reduced. Write separate half-reactions for oxidation and reduction, and balance individually.
In the Individual Half-Reactions:
2. Balance all atoms except Oxygen and Hydrogen.
3. Balance Oxygen with water, then balance Hydrogen with Hydrogen ions.
4. Balance charge with electrons.
Compare the Half-Reactions:
5. Find multiples to make electrons cancel between the half-reactions.
6. Add half-reactions together and cancel identical species, including electrons.
7. Check that all elements AND net charge are balanced.
8. If in BASIC solution, add hydroxide ions to BOTH sides sufficient to neutralize hydrogen ions in reaction. Combine hydrogen and hydroxide ions on same side to form water. Check if water molecules may be cancelled. Re-write reaction.