First, write down your characters personalities and beginning feelings (how they feel before your story begins). Then elaborate and create problems for the characters and write how they are solved throughout the story. Next create physical descriptions. Last, name them!
Now write a brief outline of what you want to happen. I do this by chapters. I usually have 1-3 sentences per chapter only explaining the main events and actions taking place.
I don't know if this is a good way to start, but this is how I do it. Lol good luck!