Wait for your deck wood to dry before you start the staining process. Purchase an oil-based stain that is water repellent and also UV repellent, containing darker pigment than your previous stain so that it will be dark enough to cover the previous color.
Use 80-grit sandpaper to rough up the glossy surfaces. Continue sanding the wood until you can no longer see or feel the glossy sheen.
Brush a coat of stain onto the railing of the deck with a paintbrush. Add a second coat after 24 hours have passed.
Stain large, flat areas with your wood stain and a paint roller. Roll over only a few boards at a time, moving in a direction so that you can exit the deck when you are finished without having to step over the area you stained. Create a film, applying the stain along the grain of the wood, while smoothing over any puddles that form as you go.
Apply the stain to more detailed areas with a paintbrush. It's important to apply the stain to all the areas of the deck.
Let the deck dry for 24 hours and add a second coat of stain with the roller.