The first thing you must do is balance all atoms on either side of the equation besides hydrogen and oxygen. Secondly add water to the side which is oxygen defecient to balance out the atoms of oxygen on either side of the equation. Thirdly add H plus atoms to the hydrogen deficient side of the equation to balance the hydrogen atoms. Fourthly add electron to the the more positive side of the equation to balance the charges. Finally multiply each equation by the required number to ensure equal number of electron being transfered in each half equation. Combine the equations cancelling common terms.