Balance the following redox equation: PbO2 + SO32- ==> Pb2+ + SO42-

To balance redox equations, do the following steps:
-Divide into 2 half equations
-Balance the formula EXCEPT for oxygen and hydrogen
-Balance the number of oxygens by adding water
-Balance the number of hydrogens adding hydrogen ions/protons
-Balance the charge by adding electrons
-Compare the half equations, and make sure the number of electrons in each is equal. If not, multiply each half equation to make sure they are
-Combine the half equations and cancel common things on both sides

With the example in the question:

PbO₂ + SO₃^2- ==> Pb²⁺ + SO₄^2-

Split into half equations: PbO₂ ==> Pb²⁺                                      SO₃^2- ==> SO₄^2-
Balance formula (not needed here): PbO₂ ==> Pb²⁺                   SO₃^2- ==> SO₄^2-
Balance oxygen:  PbO₂ ==> Pb²⁺ + 2H₂O                                 SO₃^2- + H₂O ==> SO₄^2- 
Balance hydrogen: PbO₂ + 4H⁺ ==> Pb²⁺ + 2H₂O                    SO₃^2- + H₂O ==> SO₄^2- + 2H⁺ 
Balance charge: PbO₂ + 4H⁺ + 2e^- ==> Pb²⁺ + 2H₂O              SO₃^2- + H₂O ==> SO₄^2- + 2H⁺ + 2e^- 
Equal no. electrons (not needed here): PbO₂ + 4H⁺ + 2e^- ==> Pb²⁺ + 2H₂O         SO₃^2- + H₂O ==> SO₄^2- + 2H⁺ + 2e^- 
Combine: PbO₂ + 4H⁺ + 2e^- + SO₃^2- + H₂O ==> Pb²⁺ + 2H₂O + SO₄^2- + 2H⁺ + 2e^- 
Cancel and complete!: PbO₂ + 2H⁺ + SO₃^2- ==> Pb²⁺ + H₂O + SO₄^2-