Mix a solution of water and mild household cleaner in a bucket. Use a proportion of 1 cup cleaner to 1 gallon water. Dip a rag into the bucket and wring out excess water. Go over the wood to remove any loose dirt, and then wipe the wood with a rag rinsed in clear water. Allow the wood to dry.
Wrap a piece of 100-grit sandpaper around a sanding block. Sand the wood with smooth, even strokes. Stop every few minutes to wipe away dust from the sanding with a damp rag.
Wipe the wood with a tack cloth. Wrap a piece of 120-grit sandpaper around a sanding block. Sand the wood with smooth, even strokes. Stop every few minutes to wipe away dust with a damp rag. Stop when the wood has been uniformly sanded.