Design your deck so rainwater drains quickly. Don't worry about salt spray-salt is a wood preservative. But fresh water hastens rotting.
Pay strict attention to manufacturers' suggestions when you're building decks with composite products. Don't cheat on plank spans, and follow recommendations about the appropriate tools to use.
Spring for stainless steel nails and screws. Though they cost much more than galvanized fasteners, the incremental added cost is minimal. And you can avoid the ugly stains of metal fasteners rusting and bleeding into the wood.
Also, take time to line up nail and screw heads so they're pleasing to look at when you gaze down the deck. It shows attention to detail and costs nothing extra.