Your protagonist had green eyes in book one and blue in book three. A dead character is alive in the sequel. The timeline contradicts itself. Your reader noticed and their review mentions it.
Character Consistency
Physical descriptions are the most common source of errors. Create a reference sheet for every recurring character and check it before every scene.
Timeline Management
Build a chronological timeline across all books. Note dates, seasons, and time gaps. Verify every temporal reference.
Relationship Tracking
Who knows whose secrets? Who has met whom? Track connections, alliances, rivalries, and romantic history to prevent impossible interactions.
Subplot Management
Track every open thread from introduction to resolution. Readers forgive slow resolution but never forgotten threads.
The Pre-Publication Check
Run a systematic checklist: ages consistent, descriptions match, relationships track, world rules intact. Fifteen minutes prevents permanent negative reviews.
The Complete System
For a series bible with character sheets, trackers, and a twenty-point continuity checklist, see Author Series Bible Template from IndiePress Toolkit.