Step-wise procedure for balancing redox reactions

Balance the following redox reaction:

MnO4-(aq) + C2O42-(aq) -> Mn2+(aq) + CO2(g)

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...C is oxidized.
The resulting half-reactions are:

MnO4-(aq) -> Mn2+(aq)
C2O42-(aq)-> CO2(g)

Next, balance all elements with the exception of hydrogen and oxygen:

MnO4-(aq) -> Mn2+(aq)
C2O42-(aq)-> 2CO2(g)

Then balance the O atoms by adding H2O:

MnO4-(aq) -> Mn2+(aq) + 4H2O
C2O42-(aq)-> ...