Exterior wooden decks and balconies get exposed to wide ranges of temperature variation and to the hot sun and winter rain and snow. You can prolong the life of your decks and balconies by sealing them with appropriate products. Sealing your decks will keep them looking good, prolong the life of the decks, and maintain the overall value of the home.
The first step is to clear off your deck of all the items and to sweep of the deck. You should also pressure wash your deck. Use a soft bristle brush to get up and rough spots. Let the deck dry out for a day.
You should use a product that is a deck stripper that gets up the previous sealer. Then follow the directions of the deck sealer that is appropriate for your deck and apply it evenly.
Here is a great overview video from True Value Hardware