It is a good idea for newbie Referees to make psionics exotic, at least at first, with psionically - gifted NPCs capable of some pretty strange things, at least from the viewpoint of the player characters.
I like to muddy up things and screw around with stereotypes somewhat, too, by throwing in a non-psion NPC whose "powers" stem from some highly advanced biotech / nanotech augments. That way, they can never be certain of what it is they are facing.
It is a good idea to make psionics rare at first; something scary and frightening. The NPCs could come to view psion characters as having Q-like powers, reading minds, grasping at objects across the room with telekinesis, even teleporting in and out of existence before their eyes.
To this end, make psionic - themed stories comparatively rare. Run them through plenty of normal scenarios, the usual trade, roguery and violence, and then once every three or four stories have someone turn up that they know is an active psion. The Bester, as it were, to their Garibaldi.
My favourite NPC is a Zhodani Noble who happens to be an exceptionally beautiful woman, in addition to being psionically gifted. Her presence usually means that the adventure to follow will involve a mixture of diplomacy, psionics and - naturally - violence.
Never let the players get into the mindset that only a psion can defeat another psion, though. In the end, the final happy/profitable resolution of all the scenarios lies in the player characters' hands, and even if all the NPCs are psionically capable little Darth Vaders and Yodas, it's the player characters who walk away with the loot at the end of the game, not them.