Balancing equation

Balancing equation is like a math work. It is depended on The law of conservation of mass. So that, the mass of reactants = the mass of products.
When balancing a equation, first you have to count the number of atoms of each elements.

For example, H2+O2=H2O, there are 2 H and 2 O in left hand side and there are 2 H and 1 O in right hand side. That means H:O=2:1. So for reactants H:O should be 2:1 too. So there should be 4H and 2O in right hand side and left hand side. Finally, we get 2H2+2O2=2H2O....
For some other types of reactions like single replacement, you can use a easier way to balance equation. For example, Fe + CuSO4 = Cu + Fe2(SO4)3. In that case, (SO4)2- can be seen as a whole. So you can find there are 2 (SO4)2- in right hand side. Than you can guess 3 CuSO4 in left hand side, that means there should be 3 Cu in right hand side. At last, obviously, 2 Fe in both right and left hand side. Finally the equation should be 2 Fe + 3 CuSO4 = 3 Cu + Fe2(SO3)2.
That is a my own way to balance equation. You may find a Better way when doing more exercise. Many convinience strategy will be found when you get more experience in balancing equation.