Consider the following to be a quilt of advice stitched together from dozens in your same situation. Wrap yourself up in this security blanket and make your coming out day, whenever it is, the warmest, safest experience possible.
The team at LGBT Youth Scotland have a solid 40-page guide with the good reminder to "be sure that you want to come out rather than feeling you have to." Your family, your professors, your friends, you lover of five years: none of these people are entitled to your private life, unless and until you decide they are. You can only come out to someone once, so give yourself the space and time you need to answer your own questions before you have people in your life pressuring you for answers now.
The most important step in being ready and living the good life is not what many people are most interested in talking to trans people about: hormones, surgeries or how your parents reacted.
The most important step is self-acceptance.
One of the best roads to self-acceptance is to research, research, research. Read everyone and everything you can to teach yourself the words you need to talk about yourself and your experience. Google "transgender."
Never stop sponging up data.
TransBareAll via the NHS suggests that you make contact with other people in your position. "If you know people who would understand, you'll be in a better position to tell others.”
Investigate local resources, such as LGBT centers and trans* support groups and meetups, or a local trans-friendly counselor. Crisis and trauma centers are often connected with local area resources as well. If you are in a more isolated area, the words of others who have been where you are can be a great confidence-booster.
Confidence comes from having a plan in place. Unfortunately, this means you have to get into the mindset of assuming the worst. It might dent your confidence at first to think that your parents will disown you, but it will build it up to know that you have: somewhere else to live, a job, a support network.
If you are having trouble deciding how to order your thoughts and feelings, write a letter. You can use it to turn your story into a strong, clear narrative. Mail the letter in advance of the conversation, or simply leave your audience with a copy of it after you are done speaking.
Keep a steady tone and a calm demeanor throughout the conversation, even if you have to fake it.
While becoming emotional might earn you the love of millions on YouTube, it may end the conversation with your loved ones. The more upset someone is, the less likely they are to listen. Conversely, if you are someone who rarely displays emotions, doing so can demonstrate how serious you are. Basically, know your audience. Think long and hard about how someone might react, plan for that, and then assume the opposite and plan for that, too.
Do not overshare in the first conversation with loved ones. You have the rest of your new life to hash out the nuances. For example, you may be as excited as intravenous Red Bull to tell someone the medical mechanics of gender confirmation surgery, but that is often beyond the call of duty. Focus instead on how you have felt, the steps you have taken towards making this possible, the difference between gender and sexuality, and what you want from them (ex. pronouns).
Be prepared for questions like “So, does this mean you are gay?” “Is that like a crossdresser, is it just a clothes thing?” “Are you sure?” “Have you told anyone else?” “What does your (important person in your life) think of all this?” “Why now?” And so on.
It's good to have resources to leave with them, such as PFLAG's pamphlet for loved ones. Give people room to work through their feelings and be there to talk with them when they want to. Their first reaction may not be their true feelings.
Even if they are, the people you lose do not always stay lost.
Lastly, be strong enough to know when it is not the right time, such as being financially dependent on your guardians or living with people who you know will not accept you. Sometimes, in the name of safety, you have to know when to bide your time.
HRC and Susan's have extensive information on coming out in the work place.
Transgender Teen Survival Guide is a nice spot to ask and find answers to questions like coming out as genderqueer, which you can also find out more info about here.
For non-binary people, there is this piece on coming out to parents.
Ohio University's LGBT Center directed me to several of these helpful links, including a template for coming out to your professor.
Every link in this article is itself a wealth of guides, information, and helpful resources. Take some time with them all.
You're worth it.