The most successful process I have discovered for the manifestation and sexual union with an entity is the process I will outline here. There are several steps to the process, a process similar to evocation has generally not been as workable as the a longer process to generate sexual desire and energy.

1. The process begins with a committent to the work. A period of celibacy for two weeks is ideal, which will include no masturbation or sexual release of any kind. This is important as it will assist in building the erotic energy required for the manifestation. Whether we consider the entity to be an expression of our own subconscious, an atavism as in the work of Austin Osman Spare, or something more external, does not change the importance of this stage.
2. I recommend an aphrodisiac to enhance and maximise your desire and arousal. Damiana is recommended for this, as it has several properties that are useful to this work. In his book A Manual of Sex Magick, Louis T. Culling describes an experiment with damiana in which he drank a tea made from a preparation of the heaped leaves. This had the impact of making him sexually attractive to younger women to a level he had never experienced before. I have also seen a similar ‘attraction’ effect from damiana, but its properties do not end there. I have also seen an increase in libido from its use, as well as a visionary quality also helpful for sexual trance. In fact the herb shop (or botanica) I used to buy damiana from was run by a practitioner of Santeria who expressed to me that he used it for ‘visionary dreams’.
3. The damiana will become like a daily sacrament to the working and should be followed by creation of a ritual space around your bed, or other suitable place. The choice of entity will depend upon your own approach to sex magick. The aim could be union with a deity, such as Babalon for example, or an archetype connected to your HGA or higher self. Whatever you decide the process should build in devotion and intensity as you work through the process.
4. The manifestation will likely happen when you are at the peak of sexual desire and frenzy. In my case, the first time I did this process more than 20 years ago, a green energy formed above my body as I lay on the bed. The energy formed into a stunningly beautiful and erotic female form and I experienced my mind and beyond flowing into new levels of pleasure and transcendent consciousness.