Find the masses of the elements in the compound (by weight the compound then weighing it with elements taken out). Make these masses into percentages, divide each percentage by the ar of that element and you will have the number of atoms of it in a molecule.
Carbon= % mass 80, ar 12
C= 80/12= 6.7
Hydrogen= % mass 20, ar 1
H= 20/1= 20
To find the empirical formula divide the molecular formula by the smallest number.