Changing weather conditions can punish a wood deck. All that transition from cold to hot and wet to dry makes the wood expand and contract.
The result is splintered and cracked wood, and fasteners that work loose from all of that movement. Since you don’t want your guests getting splinters in their hands or tripping over loose nails, now is the time to correct these problems.
The first step is sanding any rough edges to remove the splinters and burs. The loose nails you can simply drive back down, but you’ll be doing it again soon.
Instead, try replacing the nails with long, coated deck screws. If you drive them into the old nail hole they’re practically invisible, and they’ll ensure that both the wood and the fastener stay put.