Simplified Complexity.
That is, there needs to be plotting and scheming aplenty, but you* need to remember that this is - ultimately - Epic Fantasy. Good is White (with the occasional light shading of grey), Evil is Black (with the occasional light shading of grey, and no racial insinuations except against those of pink skin and / or tusks), and Good and Evil are in an Epic Struggle. Have been since the Dawn of Time. Can't make villians you don't want to kill, or heroes that aren't really nice people; just messes with the 'standard expected values' too much.
But you can *hide* the villian, which I did in one of the most successful games I ever ran.
(The following story is immensely simplified.)
Early on, there was a near-total party wipeout, and the survivers hauled the corpses of the dead back to the High Temple of Pelor, where the Grand High Cleric, named Father Montessi, was able to raise them from the dead, in exchange for the party's assistance with some problems in a swamp. And then, if they had the time, could they lend him a hand with... ...and while you're here... ...and certainly, I'd be happy to remove that curse, if you could...
I spent a long time, developing a very trusting attitude between the Father and the party. They were very sorry when it came time to part ways with him, as they went off on a Heroic Quest.
And then they got jumped, by villians that knew all their weaknesses, that exploited every gap in their defenses. Through interrogations, questions, divinations, they determined the Cult of Tiamat was behind it; the Dark Queen (thanks, Dragonlance!) was rampant, and intending sinister fates for the world, at the hands of her darkest minion...
...it was the moment when my "lead player" - my fiancee - suddenly realized what was going on. The snarl with which she said, "Montessi!", the look of dawning comprehension and horror on the other faces assembled at the table, as they realized that all along, they had been helping to set the stage for a Great Wyrm Red Dragon, in a clever guise as a 'high cleric of Pelor', to suddenly overthrow (several!) Good-aligned kingdoms in a fell swoop, and gain control over the majority of the world...
We - myself, my fiancee, my other players - all still recognize that One Moment, and in particular the contempt, admiration, hatred, shock, fear, and horror with which she spoke his name, as one of the greatest moments in our game.
Planning intricacy and complexity - while making sure to dumb it down (because players, all players everywhere, including me when I play, and yes, you when you play) are phenominally dumb - while making sure that it doesn't *look* dumbed down - is taxing.
But when you get a "Montessi!"-moment, it's completely worth ever second.
*: By which, I clearly mean "me", and possibly certain values of "you".