Whether you choose to use nails or screws, be sure to choose galvanized fasteners to keep them from rusting out. If you're using screws, self-tapping ones will drive in a little easier, but try not to bury the screw heads below the surface. Once the first 2 boards are in, start running the ends of the boards wild over the edge, to save on cutting time since they can be cut all at once later on. If the deck boards are relatively dry, use 16 penny nails to establish the proper gaps between the boards. Proper spacing allows moisture to drain off the deck between the boards.
Wood expands when it's wet.
If the boards are wet when you install them, you can probably butt them close together without any gap. They should shrink as they dry out and produce adequate gaps between the boards. Straightening Boards Deck boards are hardly ever perfectly straight, but you can straighten them as you secure them with a flat bar. First, secure one end of the board with the proper gap. Jam the end of the flat bar into a joist with the back of it flush with the front edge of the board.