Think about what would impress you, even as a magician, if you saw it.
If for example you saw someone throw a card through a computer screen and it came out the other end... would that impress you? If so... try and make it work.
Failing that, signed card routines are always good because there's no chance of substituting.
But also remember that certain forces and shuffles can hide a lot more than they show.
Don't forget your props either, TTs, IT, magicians wax, even a hanky to cover the crucial move for example.
And always, ALWAYS, try to think of the effect before the
modus operandi.
I have come up with a trick, but I don't know if it's entirely original, but the effect is as follows:
The jokers are removed from a deck and placed to one side, a card is shown and dealt to a spectator. The deck is shuffled, a joker is inserted randomly into the pack and the deck is shuffled again. Another card is shown and dealt to the spec. The second joker is inserted randomly into the pack and the deck is shuffled. Finally, two cards are stopped at by means of a riffle and these are withdrawn to be "extras". Upon turning over the cards in their hand, the spectator has both jokers. The "extras" are of course the shown cards. And that just came from wanting a striking effect in which jokers seemed to move about, despite being clearly placed to one side.
Come up with something simple like that - "Queens turn to jacks, queens are back in deck and jacks are gone" and then work it into a routine.
Always the best way I find.
Hope this helps!

You wont find much better anywhere and it's nothing - a rigmarole with a few bits of paper and lots of spiel. That is Mentalism
Tony Corinda