Draw 3 different reaction pathways for meta, ortho, and para substitution of a halogen (e.g. Br2 in FeBr3) onto nitro benzene. Each pathway should have all resonance structures.
After you have the resonance structures for each substitution drawn, examine them carefully and decide which set of resonance structures is more (or less stable), and decide whether a nitro-group will direct electrophilic aromatic substitution to occur at the ortho and/or meta and/or para positions (relative to the nitro group).