I think it also depends a bit what your situation is and the purpose really of it ... so, in a long term relationship I would just masturbate in front of him, because he liked that (I think liked the lack of responsibility as well) and I then had my eyes open and only yes did it with physical stimulation.
Sometimes I'd wake up in the night or something, or in the morning and he was still sleeping or just waking up, and I'd do it with my eyes closed thinking about him, then he'd just get hard and it would progress to sex.
I've had some v bad sexual experiences with him too, along the way, but of course in my fantasies it always went how I liked, so it kind of kept me in a place that was bearable. (How our minds come to our rescue to make it all ok! But denial is also such a time-waster long term - doesn't always help).
Now, though, I'm operating differently. He is gone (because was too bad in many ways) and I've had to completely wipe the memory cache of him, because any thinking of sex with him just perpetuates a pointless myth.
So now I'm exploring thinking about anything and anyone I like, which is turning out to be quite amazing! There so much you can do in fantasy that you (probably) wouldn't do in real life ...