Follow these rules.
Rule 1: Resonance structures must have the same number of electrons.
Rule 2: All resonance structures must be valid Lewis dot structures.
Rule 3: The hybridization does not change between resonance structures.
Rule 4: The positions of atoms are the same in all structures.
Rule 5: Resonance structures do not have to be equivalent.
Now try to shift lone pair or negative charge or pi bond to the next atom with following rules.