With Volumetrics, we can show light rays and we can even create fog. But Volumetric lighting increases render time.
Some times, the mesh has unnecessarily high poly count which can affect the Render time.
Environment textures, sometimes referred as HDRI, are very effective for beautiful lighting. But they can cost you render time.
Fluids can enhance the scene, but it can take longer for the scenes to render.
For high quality models, we use High Quality texture maps. But they can cost us increased render time.
Hair can be very useful in making realistic scenes, but they take longer time to render.
Using Cycles instead of Eevee. Having High Samples for Rendering. Low End PC. Using CPU instead of GPU for rendering.