Give your villains strange motivations. Ones that the players will never guess at first.
Why is the evil wizard trying to take over the dwarven mine? Well, for the gold, obviously. Except that's not it at all. There's actually some rare fungus that grows down there that the wizard needs to complete a spell that will let them open a gate to the Fungus Dimension.
Why is the vizier trying to marry the princess and overthrow the king? So he can rule the kingdom, of course. Wrong again! Turns out the vizier is from a line of druids with a mystical bond to the land, and he feels the suffering of the land under the current king's negligent rule. The best path he can see to heal the land is to gain the throne.
By making the motivations less obvious options, you set up a mystery for the players to uncover, and interesting decisions when the players finally realise the truth.
Commentary by memnarch (who has not seen the movie)
Hm, now that that's been said, that actually makes the most sense. I guess it just felt too plain to be the reason why Snoke wanted the map in the first place. Especially since there doesn't seem to be much to the place besides the dimensionally cracked slime pit, fish-people history teachers, and porgs. I do wonder why Ahch-To wouldn't have been checked as a place Luke could have been hiding out with all of the resources that the First Order seems to have. Or even just as a punishment detail for Kylo to make him check somewhere that probably won't have anything. Maybe there's something there that Snoke/Nute wants kept secret from absolutely everyone, including Kylo?
Transcript
Snoke: Before I tell you anything, let’s test your loyalties. Where is Luke Amidala?
Rey: Still on Ahch-To.
Snoke: And where is the map he made?
Rey: You... don’t know where the planet is...?
Snoke: I know where it is! I want the map.
Rey: If you know where Ahch-To is, wh—
{beat}
Rey: You never wanted to hide the planet! You wanted to hide the fact that all the maps were changed!
Snoke: Your insight serves you well. So where is it?
Rey: I thought I understood your motives, but... this is crazy.
Snoke: My dear child. You should see how many cats I own.