Step 1: Find valence e- for all atoms. Add them together.

Cl:7
O:6x4=24

Total=31+1=32*

* add an electron to the total since the molecule has -1 charge on it.

Step2: Find octet e- for each atom and add them together.

Cl:8
O=8x4=32

Total=40

Step3: Gives you bonding e-. Subtract step 1 total from step 2

40-32=8e-

Step 4: Find number of bonds by diving the number in step 3 by 2(because each bond is made of 2 e-)

8e-/2= 4 bond pairs

Step 5: Find the number of nonbonding (lone pairs) e-. Subtract step 3 number from step 1.

32-8= 24e-=12 lone pair

Use information from step 4 and 5 to draw the lewis structure.

Lewis dot structure of ClO₄^-

Alternatively a dot method can be used to draw the lewis structure.
Calculate the total valence electrons in the molecule.
Cl:7
O:6x4=24

Total=31+1=32*

Put chlorine in center and arrange oxygen atoms on the sides.Arrange electrons until each atom get 8 electrons.