I started by instructing my girlr to ask permission to cum. I'd talk her towards orgasm while we played - describing what she was feeling, and how.

That got her used to me allowing her orgasm and associated the sound of my voice with her orgasm. In other words I conditioned her to associate orgasm with the sound of my voice. The conditioning didn't take all that long (and she'd never been taken that route before - to have to ask permission to cum).

Initially I allowed her to cum immediately on request - over a few weeks, I altered that to sometimes withhold permission for a time - and force her to hold on until allowed.

Now I don't think she can cum without permission at all.

Once I'd established that 'cum on demand' conditioning I modified how I told her to cum.... When I say 'cum' softly, she has a gentle orgasm (useful for calming her after an intense session). If I snap the word out, she cums hard....and if I hum the word - holding the m - she cums extremely intensely and will orgasm for as long as I hold the word.

Volume is immaterial - I can whisper, speak normally or shout (she cums regardless, though the intensity depends on volume as well as method of speaking). She now requires no stimulation other than my voice - even in a very vanilla situation - with a look and a word I can make her cum...the word doesn't even need to be 'cum' - 'yes' works as well.

And if she is stimulated, a mere nod of my head with a look can take her to orgasm.

In many ways, trained 'orgasm on demand' is extremely easy to instill in a girl, once you work out what works for you (for the Dom). It takes consistency of approach initially - but once the conditioning is imprinted it doesn't go away