Power wash the item, especially if it is an outdoor piece that has a lot of grime and dirt caked on. A power washer will quickly clean the surface. If you don't have a power washer, fill a bucket with water and a little detergent to make the water sudsy. Dip a scrub brush in and scrub the oak wood. Let the wood dry.
Sand the wood with a medium-grit sandpaper. Sand in the direction of the wood grain, getting deep enough to expose the new, fresh oak wood underneath the faded top layer.
Smooth the wood surface, sanding it with fine-grit sandpaper. Continue to work with the grain of the wood, working in small sections.
Saturate a rag with teak oil. Teak oil brings out the natural color of wood and also protects it from weather, including sun and rain damage. Wipe a layer of teak oil all over the wood. Wipe excess oil off with a rag. Repeat the teak oil application if you want a deeper color.