Power your way to a polished finish
Some woodworkers brush on a few coats of varnish and wonder why their finish doesn't look gallery-smooth. Truth is, a silky film finish starts where the label directions stop. After the final coat cures, a savvy finisher traditionally digs out his pumice or rottenstone (powdered abrasives) and lubricant, and hand-rubs the finish to an even sheen without dust nibs, runs, or a "plastic" look. If that process seems time-consuming and messy, you can see why most guys rub out only horizontal surfaces, such as a tabletop, where light best reflects off the finish.
For a faster, cleaner method, try the techniques used by auto-body experts. Instead of oils, powders, and handheld rubbing blocks, they use premixed automotive polishing compound and a foam buffing pad on a dedicated polisher. You can achieve similar results using your random-orbit sander.