The following is a list of basic principles related to reading chemical notation and balancing chemical reactions. Mastering this list and fully understanding it is a great stride in mastering the ability to balance equations in chemistry.
When balanced, the number of each atom is the same on each side of the reaction—the reactant side and the product side.
You cannot change subscripts to balance a reaction.
You can ONLY change coefficients.
The subscript applies ONLY to the element that immediately comes before it and tells how many atoms of that type are in one molecule.
The coefficient comes before the molecule and tells how many molecules are present. Multiplying the coefficient by the number of any atom in the molecule tells the total number of that atom present.
IMPORTANT: Correctly balanced, the coefficients will always be the SMALLEST possible numbers—not multiples—that results in having the same number of atoms on each side of the reaction. It is like finding least common denominators and reducing fractions. For instance, if the equation balances with the coefficients of 4, 6, and 2, then it would be proper to "reduce" that to 2, 3, and 1.