Sometimes the hardest part of writing a novel or story is getting it started. If you feel stuck, work on developing your characters individually. This not only can get your creative juices flowing, but inspire new ideas of how they fit into the story and contribute to the plot.
Every story should start with a premise, which can usually be stated as a “What if?” statement. How that is developed will be further explored in a basic outline, which can lead to a chapter outline.
This is not a necessity. All authors develop their own style, not only of how they put words on the page, but how their story gets written. Some maybe start at chapter one, page one, while others may write the epilogue first, or jump all around as their muse dictates.
Don’t force yourself into a modus operandi that doesn’t feel comfortable. Trying them all when you first start out, however, will help you find what fits your style. Once that is identified, you’ll discover your own ways of overcoming writer’s block.