Boards run parallel to the bearer and perpendicular to the joists.
When attaching the boards, use galvanised fasteners to prevent corrosion, which can cause major problems.
A stringline is tied between a nail on the joists at either end to make sure the first board is straight. To ensure even spacing of decking boards, tap a 3mm nail into the joist next to each board. This guarantees a 3mm spacing. Draw a line across the boards above the joists and use it as a guide to keep the nails straight.
When joining decking boards, make sure the join is directly over the centre of the joists. Also remember to stagger the joint so they're not all in one line. Be sure to drill holes for the nails, angling them in towards the joist to keep the boards tight. You can cut the overhang straight, or you can create a gentle curve by marking a curved line with a piece of conduit or garden hose.
Clean up the end of the boards with a block plane, a sanding block or an orbital sander.