How abot this then:
I put an electric plug in your ass with high enough settings to be really painful and make you scream of pain.
Put a strong remote-control vibe on your clit and in your pussy.
Then gag you, Blindfond you and wrap you up in tight something like this:

but leaving your breasts and feet open.
And you will spend at least half a day like this, completely helpless and so tight that you can't move, while I have options to shock your ass, make you cum (or tease you) with vibration, play with your breasts or torture them, tickle or hurt your feet so that you are almost crying... All that while you are blindfolded, gagged, helpless and not even able to move one limb. Not even able to beg for it to stop because you are gagged*.
Maybe I'll turn the vibe on for hours. Maybe I'll pour hot wax on your feet and breasts while you can't even squirm. Every shock to that ass will bring tears to your eyes, but all you can do are muffled moans through a tight gag and face mask. And sometimes everything stops, and you are left there, not knowing what will happen next and when it will happen.
By the end of it you will be willing to do anything I ask and I'll ask it. And you'll do it good, if you don't want to return to the predicament you suffered through.
*I'm a sane person though, so you are safe because I won't take my eye off you for one moment.
Is that more to your liking?
forced to train to become, say, the best fellatrix ever, how would you proceed?
Well, after a few hours I'd ungag you and see how you manage. And I think you will be pretty eager to learn, because you know that if I'm not satisfied - you will be gagged again and your suffering will continue for one more hour, until you are ready to try again. I'll make sure to read on the subject, and will even be generous enough to provide you with some tips while you suffer. Yes, I think you'll make it right after 4th or 5th try...