Two hydrogens contribute 2 and two oxygens contribute 12.
Use H–O–O–H connectivity.
Hydrogen must remain terminal.
Draw three single bonds.
The H–O, O–O and O–H bonds use 6 electrons.
Place two lone pairs on each oxygen.
The four lone pairs use the remaining 8 electrons.
Verify formal charges.
Every atom has formal charge zero.
Why there is no O=O double bond
Each oxygen already has two bonds and two lone pairs in H–O–O–H. Converting the O–O bond into a double bond would exceed the 14-electron budget or require incorrect charges.
2D versus 3D
The Lewis diagram is often drawn flat, but the real molecule is nonplanar. Each oxygen has four electron domains, so the local molecular shape around each oxygen is bent.
Common mistakes
Using H–O=O–H connectivity.
Putting hydrogen between the two oxygens.
Adding three lone pairs to each oxygen.
Assuming the flat Lewis drawing is the full 3D conformation.