Look for fascia boards starting to warp or separate at corners and repair
Look also for water pooling on certain deck boards. Warped boards can catch
water and prevent drainage causing rot to start.
If it is a minor warp then use a belt sander
and carefully sand the board flat. Otherwise remove it and flip it over.
Keep an eye out for any soft spots on the decking boards
where you notice water pooling and particularly if there are nails set
below the deck surface. These spots are candidates for premature rot
Fill all nail or screw holes on deck boards with an exterior wood filler
or even an auto body filler (if you cover it with a solid stain). Never let water pool in these little holes.
I think you get the idea. If you want your wood deck to last, cleaning it requires a thorough approach.
Some Other Essential Reading: