2 NaOH+H2SO4 ----> Na2SO4 + 2 H2O
To balance any chemical equation, we always obey the law of conservation of mass.
Starting from first element (i.e. Na in this case ) check if the number of atoms in reactants and product are same.
If you encounter any lack then multiply it by any number so that there are equal number of atoms of that element both side.
Mind it that this is a hit and try method , practice more and more only then you can solve these