4 ideas
Each life is sorted into fixed categories rather than told as a sequence: ancestry, omens, career, public acts, private vices, appearance, habits, death. Virtues and vices sit in separate blocks, so the reader judges a ruler by weighing the two lists rather than following a story of development.
The life of Caligula first lists his acceptable acts as emperor, then turns with the line 'so much for Caligula as emperor; we must now tell of his career as a monster.' The second half catalogues his claims to divinity, incest with his sisters, the plan to make his horse Incitatus consul, and his wish that the Roman people had a single neck. He was stabbed to death by officers of his own Praetorian Guard in AD 41.
The ruler's true character is read from the body and the household rather than from policy. The result equates tyranny with uncontrolled appetite, so a ruler's excess at the table or in bed stands in for his abuse of the state.
Suetonius served as an imperial secretary under Hadrian and had access to the archives, so he could quote Augustus's own letters word for word. He places these documents alongside anonymous gossip introduced with 'some say' and 'it was rumored,' usually without deciding which is true.