Prepare a new maple surface by sanding with 150-grit sandpaper, stroking gently with the grain of the wood. Remove dust by vacuuming or wiping with a tack cloth.
Working from a small bucket, load your brush with polyurethane, wiping excess liquid from the brush onto the inside of the bucket. Apply the finish in long strokes with the grain. If you miss a spot or see thin sections, don't touch up. You'll leave brush marks behind.
Allow to dry overnight. Sand with 220-grit sandpaper to remove imbedded dust. Remove the dust as before.
Apply a second and third coat, as necessary, sanding between coats, but not after the last.