How should I properly apply polyurethane to my project, including the necessary steps of sanding between coats of polyurethane?

To properly apply polyurethane to your project, start by sanding the surface with fine-grit sandpaper. Apply a thin coat of polyurethane using a brush or cloth, following the wood grain. Let it dry completely before sanding lightly with fine-grit sandpaper. Repeat this process for 2-3 coats, sanding between each coat for a smooth finish.