Your story is designed to tell the reader about something extraordinary that happened to the character. Usually it involves a change or journey, separated from their normal and dull routine. Yet that routine shapes their behaviour and response to the new events, being itself shaped by the character’s past. If you want to convince the reader you have to understand what the character was like before the story begins.
To do this you have ask what is a typical Wednesday afternoon or Friday Night for the character? Make it a week or a month and plot out a diary. Who do they interact with? What do they eat? Detail their usual routine, however mundane it might be. Most of this will never be seen by anyone else but little details can be the difference between generic characters and memorable ones.
Ian Fleming told us a lot about James Bond’s food and drink habits, details largely irrelevant to the plot. This helped make the character more believable, allowing readers to picture him in extraordinary and often unbelievable situations. Let your characters exist outside of your story.