The general opinion by the end of the nineteenth century was that to do Magick a person was strongly advised to "live" an ascetic and non-sexual "life". A man named Aleister Crowley fortunately provided an alternative to that enormously tragic misunderstanding and teaching.
He scrapped it altogether. And even though there still are people who cling to the foolishness of the "esoteric orders", his legacy is felt both among eclectic witches and magickians, and among those who strive to return to the pre-christian traditions of Nature Magick. Many neo-pagans are very sensible persons and don't give a fuck about present day society pietistic, anti-sexual, anti-Life definitions of anything.
Sex is quite simply a completely natural act that should be enjoyed and enhanced at any leisure… as is Magick. Doing the two in tandem enhances both beyond the sum of the parts and is something of a high point of human Life…   It's the means and the ends both.
In other words: Sex-Magick is very, very Powerful.
Before you (the rite-master) begin you must realize that the other participants aren't there as objects, but as participants. They must themselves realize this. Both a low and inflated self-image is a bad path to Magick (and everything really). You're the Guide. The guide isn't necessarily necessary, but it can be useful and also downright essential in some (potentially dangerous) situations.
I'll cover both dark and white Magick here, since I've never really accepted the distinction. I'll in fact cover any area I know of eventually, since I've never allowed myself to be held back by any such limitation.
This, as the rule of three and other, similar silliness is just human inventions and has no bearing on Reality. Reality doesn't fit into our limited perception of it. Fortunately not. And Reality is what we're dealing with here. Magick is Reality.
You may call it hyper-reality, if you wish, but in my opinion the addition is unnecessary really, adding nothing significant to our further understanding.
Any sort of stimuli (such as Bella Donna) can be used in advance. Even if it isn't really necessary it can serve as a way of killing a fit of nerves.
Building sexual tension and energy shouldn't be too difficult for someone with a minimum of imagination…
Magick is moving energy, moving reality… or rather our perception of it, moving ourselves to a better viewpoint, thereby liberating what is resting inside, making Phoenix rise from its ashes, making us able to influence the manifestation of Reality. A magickian, a witch is a Ghostdancer, one moving the world, an Agent of Change.
Art, like Life can't be defined, but must be experienced.