When I built my deck several years ago, I used 2-by-6s instead of the typical 1-inch decking. And because of some bark left along the edges of the planks, I put them on the deck 'upside-down.'
If you look at the growth rings in the end of the planks, imagine that you're looking at the end of the log before it was sawn into boards. Which broad side of the plank would have been closest to the bark? When you use the planks on a deck, you want that side facing up. If you put the boards on the deck the other way (like I did), they'll have a tendency to 'cup' or slightly curl.
This is a bad thing on a deck surface, because cupped planks are less likely to shed water, which can shorten the life of the deck. (By the way, this isn't such a problem for quarter-sawn lumber, but it would be very unusual to use quarter-sawn lumber for decking because it's more expensive.)
Partly because of my poor design, but also due to natural weathering, it's time to refinish my deck. I started last week by cleaning the deck and wetting it with plain water. Then I sprayed it with a mild acid cleaner made specifically for this purpose. The acid removes mold and thoroughly cleans the surface of the deck. After working the acid into the surface with a stiff brush, I allowed it to work for about 40 minutes before thoroughly washing it off (again, with plain water).
My plan was to stain the deck after two or three days as recommended by the manufacturer, but we've had intermittent rains, so that hasn't happened yet. If this keeps up (I'm not complaining; we need the rain), I may have to use the acid wash again prior to staining the deck.
More updates next week.