I've been playing VC for quite a while, but I never realised that Terror seems to be playing an important role in this Army.
Many VC-Players I know use Wraiths and th Black Coach only because they cause Terror.
But when I used it I never seemed to have any luck at all, it didnt really work out <_<
So are there special tactics or suggestions how to use Terror "the right way" to achieve victory?
I'd like to play a Wraith but I've never found a way to make use of it, because he isnt such a great melee-heroe.
Any suggestions please? :)

I can't say that I've ever taken a terror-causing model for the sake of Terror.

I take a wraith because he's a great character to have holding the Cursed Book in a unit of zombies. It creates one very useful holding unit. Two S5 attacks isn't exactly a bad thing, either. I rate this set up for a wraith very, very highly. I'm currently running him in a unit of Grave Guard with War Banner. Due to the Cursed Book, this unit can often win combat even without causing any casualties.

I take a Black Coach for its abilities as a flanker, the potential damage it can do on the charge and the psychological effect having such a large, powerful model on the table can have on your opponent.

You can't rely on Terror to do what it is supposed to do. You should formulate your plans to assume that your opponent is going to pass all his Fear and Terror tests. That way, when he does fail a Terror test, it will be a good surprise rather than a bad one. Ok, it may mess with your plans a little bit, but one of his units is running away, which is a good thing, right?

Cheers,
DLJ