Use a sponge sander to rough up the surface of the table top and legs. Sand lightly -- it is not necessary to remove all of the paint or stain. Wipe the table down with a tack cloth to remove the sanding dust.
Turn the table upside down on the drop cloth. Use a foam paintbrush to apply an oil-based primer with a sealer to the table legs. Let the primer dry thoroughly.
Turn the table right side up. Apply primer to the table top with a foam paintbrush. Let the primer dry thoroughly.
Turn the table upside down on the drop cloth. Use a foam paintbrush to paint the table legs. Apply two or three coats of paint, allowing each coat to dry completely between applications.
Turn the table right side up. Paint the table top using either a foam paintbrush or a paint roller, for smooth surfaces. Apply two or three coats of paint. Let each coat dry completely before applying the next coat.
Apply water-based polyurethane to the entire table, using a foam paintbrush or synthetic bristle paintbrush. Allow the polyurethane to dry. Lightly sand the table with extra-fine sandpaper. Wipe off the sanding dust with a tack cloth. Apply a second coat of polyurethane in the same manner, letting it dry, then sanding and wiping the table with the tack cloth. Apply a third coat of polyurethane. Let the finish cure for several days before using the table.