Our mumming is drawn from several different British traditions:
We use two forms of mumming. The first is dramatic re-enactment of a symbolic moment from myth. Costumes are used - either elaborate, or very simple - and performers can use dance, or a script, or a combination. This can be used to express the will of the witch: Lugh fighting Crom Dubh for the harvest as part of a ritual to make a harvest happen. If an individual is trapped in a hopeless situation, let them take on the role of Brigid returning summer to the world as part of a rite to aid them. Or it can be simple celebration - like a nativity play, a way to re-tell the old stories dramatically. In some rites, one or two individuals can take on the persona of a Power, and interact with the rest of the group. We read in the God of the Witches that each coven had a "Man in Black", who was mortal but also in some sense a stand in for the devil himself.
By performing these symbolic rites, we can attune ourselves to the land, honour the Powers, and tell stories. Remember that trick or treating is also a form of mumming - it doesn't have to be complex or hard.
The second is far deeper. In these, we attempt to genuinely draw down the spirit we are impersonating, to empower our rites. There is no shortcut to that kind of power, although it has been seen all over the world - in vodou peristyles, in norse beserkers, in Wiccan High Priestesses, when Christians speak in tongues. Trance states, ecstatic dancing, fervent belief, drug use, hysterical atmospheres - all have all been used.
I have no idea how to accomplish any of these things. My hope is, that by practicing make-believe we will in time develop the ability to do it in actuality. I'm not sure that drawing down is a thing you can do as a mage who works on a symbolic or a-theistic level - you really do have to believe.
Traditionally, some members of a community only have been empowered to do drawing down rites. Fuck that noise. Good working groups don't have one Lady or one Priest who has the ear of the gods. If you run a coven, allow all members to take on roles in mumming, and ensure that "starring roles" don't go to the same few people. When devising rituals, get everyone involved, and let people raise ideas of particular stories they wish to explore.
I think - traditionally - this is due to the "danger", the danger of not coming back to yourself, or it being a skill which takes many years to develop. For this reason, only highly skilled and trained individuals undertake it. I'm making this religion up at my kitchen table, surrounded by my unpaid bills and unwashed crockery. I'm not an initiate of anything. I have no secrets or wisdom to pass on, no inner temple to introduce you to - only a belief that everything we see in Wiccan and post-Wiccan paths can be done powerfully, without making reference to gender or sex. I'm in no sense an elder who can pass on this information. I am myself developing my skills, and perhaps one day I'll have more to offer than - people internationally and throughout time have had these direct experiences, and they are as open to us as to anyone.
Balance reading and research into these experiences, with devotion and attention to your Court. It may be effective to write a brief chant or set of habitual actions you use to draw the spirit towards you. I like this article very much.
You can and should attempt this as a single person. You could turn your myth into a series of stages, where you speak certain words or perform certain actions at each point. You could do it as part of a walk, or part of a dance. It's probably easier to do this NOT as part of a coven, because it's less socially awkward.
Some people are shy. Mumming is not compulsory. There are many ways to serve the Powers. I think mumming and channelling make intuitive sense in the history I'm drawing from. Shy members of a group can take on non-dramatic roles in group work; shy solo witches can try other things entirely. Mumming doesn't have to be complex or intense, however - donning a flower crown and speaking the words of the Charge of the Goddess is a great start.