It’s good to be present in the moments of your life, and it is also good to be present in the moments of your story and your character’s lives. That’s it. You want to communicate to the reader who your character is then what they do, what they see and don’t see, think and don’t think, feel and don’t feel, is everything. Sure, you can roll in backstory, their past, but even here what’s important is how whatever happened in their past made them feel and think and how that shaped them. I had two grandmothers: both of them were poor, uneducated, and married the wrong men. One was bitter and that bitterness filled whatever room she was in. The other was joyous, interested, funny and that filled whatever room she was in. My point: to make you understand each character what happened to them isn’t enough. To make your reader’s understand what happened to them isn’t enough. You have to show the reader their inner lives.
I think you do this by being present in the telling/showing. You try to express to the reader what the character’s reactions are to what is happening in a scene. You get in your character’s mind and you make things happen and you work to make sure your character’s actions and reactions —physically, emotionally, and intellectually— are authentic. That’s how you build a character your reader will want to read about.