Lewis structure give the connectivity between atoms in amolecule.they tell about the arrangement of of the atoms of a molecule with in 3 d space...
1.Determine the total number of valence electrons in a molecule.
2.Draw a skeleton for the molecules which connects all atoms using only single bonds.
3.Consider the remaining electrons and place them so as to fill the ocets of as many atoms as possible.
4.Fill the remaining ocets by making multiple bonds.
5.Check that you have the lowest formal charges possible for all the atoms.