Electron donating groups (EDG) with lone pairs (e.g. -OMe, -NH2) on the atoms adjacent to the p system activate the aromatic ring by increasing the electron density on the ring through a resonance donating effect. The resonance only allows electron density to be positioned at the ortho- and para- positions. Hence these sites are more nucleophilic, and the system tends to react with electrophiles at these ortho- and para- sites.