Practical thoughts:
1) actively encourage trans people into your community and spaces. Be explicitly clear that they are welcome.
2) promote and enforce robust codes of conduct, and ask for this in events to which you contribute.
3) report anti-trans content to your own instance admins, and to the hosting instance admin if it makes sense to do so.
4) buy stuff (if you are in a position to do so) from trans people. Loads of trans people in the fediverse have small shops selling cool bits and pieces (drawings, books, jewellery, and more).
5) if you control the design of forms and systems, do not collect gender information unless necessary (and I don't have a good example of when this might be, but someone might)
6) push back against laws and policies which discriminate against, or make life harder for, trans people. Write to your MP, and be vocal in your support.
#TransDayOfVisibility