Pretty broad question, and probably what should define and steer your game development. Here's are some generic (albeit time-honored) goals:
1) SURVIVAL: We all must get out of here alive against (alien invasion, zombie apocalypse, demonic possessions, etc)
2) DEFENSE: To preserve our happiness, we must fight against the overwhelming threat of (invading empire, sand worms, oppressive school teachers, etc)
3) ACQUISITION: We would really like to have that amazing thing, the (hidden treasure, artifact that belongs to somebody else whether they deserve it or not, magical pillars of all that is right and good, etc)
4) EXPLORATION: We are deeply interested in discovering the secrets of the (underwater city, ancient ruins, deep space we have been stranded in, the hidden fantasy world within the wardrobe, the magical city that has been sealed off for a thousand years)
5) COMING OF AGE: I know you don't think much of me, but by the end of this story I will be (a powerful wizard, the previously missing heir to the throne, Prom Queen, etc)
There's several more, but hopefully one of these arcs strikes your fancy!