I have the same issue with my wife, she is very vanilla in bed with little motivation to try anything different. I am constantly trying to draw her out, maybe use toys or dress up. The key is comfort, how comfortable are they with you, I would think in this situation you will need to be the aggressor. Statements like " I was reading in Cosmo about this new position will you try it with me? " or " I want to do this with you" or " I want you to do this to me". It will ultimately come down to how important the relationship is to you and how much time you want to spend on it. Watching someone blossom sexually can be an amazing experience their confidence in the bedroom will translate in to so many different facets of their life and you helped them get there. Good luck !!
Its not about making them into something better, its like food, you can introduce them to it, but you can't make them like it.
As for they can't please you in bed, maybe you need to let them know what pleases you.
I was once a young guy with no real idea, but from my experiences I have grown into something a little different to that, because I found things I liked and developed them. I also learnt things in my day to day life that have shaped me and the way I interact with people.
But the problem with saying they are not as good, or making them better, that will just make someone feel worthless and clam up and not want to lean new things.
never thought of this, but i gess die hard vanilla addiction is hard to beat, be it ice creme or sex!
My best suggestion is: TALK! Try asking simple questions like what turns THEM on and off. What they've fantasized about. If they LIKE porn; and if so WHAT KIND. the more you learn about flipping their switches and USE it to do just that; the more willing they will be to reciprocate!