Your notebook is gapes open with scores of ideas scribbled in no particular order - organized chaos speaking volumes to the author. An outline beckons you to fill in the gaps and fatten its skeletal framed entity into a fat, juicy story.
...Now for the fun part....
Today is a day of genesis - the birth of your characters. In stillness, take your mind and spirit to sit with the main character of your story. What does he/she/it look like? What is their scent? What does this character eat? How do they cry and what do they laugh over? (or can that character laugh?). Describe every single detail as if you were living that character's existence. Experience in completeness the very being of the character.
Write it down. Write and write and write until each and every nuance of that character is recorded.
Then do it again...with the next character and the next. Be sure to leave space to include detail that may inadvertently crop up as the manuscript unfolds. Keep intricate notes and know these characters intimately. It's imperative!
There is very little that will be as rewarding as the actual creation of the characters in your story. You assume great responsibility, almost altruistic in nature, when you create these beings. You are meant to relish the experience, savor creation at its fullest. Enjoy!