How should I properly prepare a surface for applying water-based polyurethane by sanding?

To properly prepare a surface for applying water-based polyurethane by sanding, start by sanding the surface with a fine-grit sandpaper to smooth out any imperfections. Make sure to sand in the direction of the wood grain to avoid damaging the surface. After sanding, clean the surface thoroughly to remove any dust or debris before applying the water-based polyurethane.