Take all furniture and removable plants off the deck. Wet down any surrounding plants and cover them with tarps so you don't rinse off cleaner onto them.
Sweep off any leaves or other debris and use a shop-vac to clean out sand and dirt from between the boards. Hammer down any nails that are sticking up and sand any areas that are rough or splintered. If any boards are badly warped or damaged, replace them.
Check the bottle of cleaner and see if it requires the deck to be wet or dry before beginning. If it's a concentrated cleaner, follow manufacturer's directions for mixing. Place in a dish bin or something that can accommodate your broom.
Apply the cleaner with the broom and don't let it puddle anywhere. If you have a large deck, only do a section that you can keep wet with the cleaner. The cleaner needs to soak into the wood and normally takes about 10 minutes. Don't let the cleaner dry.
Rinse the deck thoroughly after allowing the cleaner to soak in.
If you have any tough areas to clean, go back over them with a hard bristle brush. Don't use a wire brush on a deck as it can damage the surface or parts can break off into the wood.
Rinse off all your equipment with warm water and soap. Rinse off the tarps before removing them from the plants. Allow at least 2 days before staining the deck.