Story Plot Help

[Ace]

Hey,
currently I'm working on a story for my game. But somehow I got a blockade in my head. I can't think of a nice plot for my game.
So far I came:

There are 4 guys. They are going on a journey and leave their home, a little isle, to experience some adventures. With a ship they're moving to a big city.

Of course I wrote this longer and with some stuff, but this is how far I came.

Now I need some ideas, what could happen to them. I need a primary target, what they want to reach with their journey and maybe some smaller problems on the way to solve it.

I hope someone could help me, as I'm stuck with that for almost a month now^^

Thanks in advance!