To optimize level streaming in Unreal Engine for seamless transitions in a large game world, ensure organized level design with distinct areas, utilize Level Streaming Volumes for dynamic loading, set up level details appropriately, optimize assets for performance, consider asynchronous loading, implement pre-loading for anticipated areas, and employ custom Blueprint or C++ logic for dynamic streaming events. Optimize lightmaps, dynamically adjust streaming distances and priorities, and test regularly on target hardware. Include loading screens or animations, monitor and optimize CPU and GPU performance, and update navigation meshes for AI. Document your setup and collaborate with your team to ensure efficient development and maintenance of a smooth player experience.