So, you have settled on a niche and even filled a few pages of a note book with a stream of un-edited musings.
At this point, you should definitely keep writing and push yourself to write more today than you did yesterday.
Also, you should go back and read what you have written. You will begin to notice a gradual improvement in your style of writing and a lessening desire to edit what you have written.
Look for recurring themes in your writing. Is there a topic you are particularly fond of writing about?
Note the tone of your writing. Is it dark and sad, funny, or happy and upbeat? Are you writing prose or poetry?
Look at your choice of words. Are they appropriate? Do some words appear repeatedly? Open your Thesaurus and look for alternatives. Make a point of remembering to use these new words the next time the opportunity presents itself.
Your next step will be to narrow your focus on to a single theme or topic.
As you continue to explore your chosen subject, you should do some research. See what others have already written about it, then examine it from a new angle.