Most of us would naturally like the spaces that we inhabit and create to be inclusive of a broader range of humanity, especially marginalized people. I've met plenty of ritualists and event organizers that want to make their spaces more friendly and open to trans and nonbinary people (trans being a general term for people who aren't the gender that they were assigned at birth, and nonbinary specifically for those who are neither men nor women) but they don't know where to start. Far too often they assume that simply saying, "All are welcome" means that people of all sorts will feel welcome to attend.
If you simply say that everyone is welcome without understanding what would make people feel welcome, it looks like you're trying to make a show of being accepting without really doing the work necessary. Trans and nonbinary folks are used to being unwelcome, and we're used to being in spaces that aren't shaped in such a way as to fit us, as modern society still keeps us on the margins at best. It doesn't help to say, "Come on in" when the inside is just as hostile as the outside. That's rarely the intent of those who do it, but intent isn't the same as impact.
There is a long history of exclusionary behavior and attitudes in Pagan and adjacent spiritual spaces that makes many trans folks extra wary of them. Sometimes the intent is to exclude, but more often than not the things that make a space exclusionary are background assumptions that cisgender (people who aren't trans) folks don't end up considering, because they involve things that they don't need to confront in their daily lives.
Something I like to say is, "Everyone deserves to see themselves in the stars." Human religion is human-shaped, and when we conceive of divinity, we conceive of it in ways that are similar to us. Whether it's a lone deity or many, they are ascribed characteristics by humans that are human, because human things are things that we understand and can connect to.
When your concept of divinity is one that, by the way that it is described and the way you describe it and interact with it, excludes certain kinds of people, you are making a statement about those people whether you want to or not. When cisgender men and women create religion in which divinity looks and acts exclusively like they do, they are creating spirituality that says, "These kinds of people are divine, these kinds of people are worthy, these kinds of people are reflected in the highest beings in the cosmos." Which is fine for them, but leaves out the rest of us.
Gender is something that humans create. We decide, collectively, on what is masculine and feminine, and reinforce these categorizations socially. If the divine has a gender, it is because humans have decided that it must, and if it is something that we have decided and assigned to divinity, then we can also change our approach to that to make it more open to more kinds of people.
You can start at the root of things: your cosmology. The cosmology of your spirituality will inform the assumptions around it, the practice of it, and the social environment of it. Generally speaking, the idea of a Divine Masculine and a Divine Feminine that don't include the possibility for divine gender that transitions, that changes, that can be both in one or none of the above is going to be a vision of divinity that excludes trans folks. If we don't see ourselves reflected in your vision of the cosmos, then how could we feel welcome?
I don't personally believe that masculinity and femininity are intrinsic cosmic concepts that are linked to the human manifestation of gender. I think that gender is important to us, and as such, we view different aspects of existence through this gendered lens. As above, so below: where is the Divine Androgyne? Where is the Agender Divine? Where is the Fluid Divine, the liminal Divine? If you're going to gender the divine with human genders, then simply be open to other understandings of human gender than the ones that you participate in. Include them in your descriptions and in your rites. Having an expanded understanding of how the divine can manifest can only help you spiritually.
People describing energies as masculine and feminine also has a well-established history. Often people get labeled with "masculine" or "feminine" energy based on their birth-assigned genders. That can be really problematic with for trans and nonbinary people, and a microaggression that is often used to justify excluding us from spaces and rites. As noted with deities above, if your conception of gendered energies is rigid, unchanging, and binary, it's not going to be one that contains a genuine richness of human experience. Remember, we are part of the universe, what is without reflects what is within and vice versa.
This leads me to the next point I'd like to share, and this is about human interaction: learn to listen to trans folks when we talk about our experiences, especially in regard to gender and spirituality. There are many deities and spirits that have obvious associations with trans folks due to them having stories wherein their gender changes or because they are witnessed as different genders at different times. Trans folks tend to have complex and highly idiosyncratic understandings of gender, and sometimes the obvious choices aren't the best ones. If a trans person feels a connection to a narrative of a being that doesn't seem obvious, listen to their reason why. It doesn't need to reflect on your own connection to and understanding of that deity or spirit, but trying to understand can definitely improve your own understanding, not only of trans experiences but also of the being in question.
This also applies to ancestors and ancient peoples. The experiences that we describe as transgender have always been a part of humanity. There are many societies in human history where people we would describe as trans and nonbinary were recognized for their sacred liminality and unique perspectives. Frequently when studying ancient societies, trans and nonbinary folks see references and feel connection to other people who seemed to share similar experiences and outlooks with regards to gender. When a trans person speaks about trans ancestors, listen to them and understand that they are making a connection to an ancient, powerful, and deeply sacred part of human experience. We know our own, we recognize our own; do not discount us when we see others like us and bring that forward into the conversation in the modern day.
Understand that gender is not anatomy. There are men with wombs and women without them; if you are conducting rites or holding groups based on shared physical, anatomical mysteries, do not label them by gender, but find other ways to describe them. Insisting that mysteries having to do with a uterus are "women's mysteries" others men and nonbinary folks with that anatomy, including them in the category of "women" when they are not women. There are other ways to word these things, and if you're having trouble finding ways to word it, reach out to trans people who may be interested in these things and ask for their opinion and understanding of it; we are often happy to help when there is a genuine desire to make spaces more accepting of us.
Our understanding of divinity is human. When we look to the divine, we inevitably project human shapes and concepts onto it. We can't help that; we only have our own perspective with which to work. Humanity is not a single perspective or thing; however, it contains a rich tapestry of experiences and realities to draw from. Applying a rigid binary to the living cosmos itself is like painting half the sky pink and half the sky blue; it's convenient for separating things into two categories, but it leaves out the underlying complexity. Listening to and considering the words of those whose experience with gender is different from your own can only open doors to a deeper, more nuanced, complex, and ultimately fulfilling connection to the cosmos, as well as making a space where trans and nonbinary people feel as at home as you do.