To improve a bad first draft novel, focus on the characters. Develop them more fully. Give them clear motives, desires, and flaws. You can also add more details to the setting. It will make the story more immersive. Another tip is to cut out any unnecessary parts. If a scene doesn't contribute to the overall story, get rid of it.
First, read it through objectively. Look for major plot holes, inconsistent characters, or unclear themes. Then, start by fixing the plot structure. Make sure the story has a clear beginning, middle, and end. For example, if your first draft jumps around too much, re - order the events to create a more logical flow.
Well, one way to enhance a bad first draft novel is through getting feedback. Share it with some beta readers or writing groups. They can point out things you might have missed. Also, work on your writing style. Vary your sentence structure and word choice. Use more vivid and descriptive language. For instance, instead of saying 'the sky was blue', you could say 'the sky was a brilliant, cerulean blue that seemed to stretch on forever'. This will make your novel more engaging.