Start with the role in the story
Write down what the character wants, what prevents them from getting it and what they risk losing. These three points are often more useful than a long list of tastes and favourite colours.
Keep continuity details
Age, appearance, injuries, important objects, speech patterns, family links and frequently visited places are useful when they need to remain consistent across many chapters.
Track relationships
A relationship is not static. Note its starting point, the events that change it and the expected state at the end of the story. This helps make development believable.
Update the sheet while writing
A character sheet is not only a planning document. When the character develops or a writing decision changes, update the sheet so it remains a reliable reference.
Put these ideas into practice in one workspace
The callen-jf.com Writing Studio lets you move directly from advice to practice: write, structure the manuscript, prepare characters and chronology, then export and format the book. The account is free and the tool remains separate from the public pages of the site.