I did a lot of coming out by email, especially for people that I seldom see. For those I knew would be accepting, I took a lighthearted approach: "I am announcing my resignation from the male gender." For those I was less sure of, I started by describing how I never fit in, then about being diagnosed with gender dysphoria, then finally using the T-word and announcing that I was transitioning.
For several people in similar circumstances, I did a lot of cutting-and-pasting, though I personalized each letter a bit.
There is no right way to do it, no one size fits all package. You know your friends and relatives and you will be able to anticipate their most likely reactions.