Depending on your budget, stay on the mid-priced south coast or the fancier west coast, chilling on the beach before going diving or snorkeling (maybe surfing in the south) and spending an afternoon wandering the island’s heart: Bridgetown.
On the fifth day, take a sailing cruise up the west coast before spending a couple of days exploring the interior and the east coast, visiting botanical gardens and hiking along remote unspoiled beaches alongside crashing waves. This will give you time away from crowds plus time partying with crowds.
Do the same as a one-week visit, but with more time to utterly chill out. Take roads at random. Get lost! Head down to the rarely visited southeast to explore tiny hidden coves, or north to the cliffs of St Lucy.