Well, start by imagining a unique setting. Think about the geography, the different races or species, and the magic system. Then build the rules and history of that world.
The key to world-building in a fantasy novel is to be creative and consistent. Develop a backstory for the world, define its cultures and religions. And don't forget to make it all feel believable and coherent.
To world-build for a fantasy novel, you need to focus on several aspects. First, create a detailed map to visualize the layout. Next, establish the social structures and politics. Also, come up with interesting creatures and mythologies that make the world rich and immersive.