You do good quest, donate your personal gold to the royal treasury, keep your promises to your followers, be friendly to everyone, kill bad guys etc. It's much like RL.
Also you can get a weapon that gives you morality in Fable 3. Kill evil enemies and giving to the poor as well in F3. In F2 however, it usually just involves being nice to everyone, donating to the Temple of Light, gifting (money/stuff). General good deeds is what I'm saying.