Here's what I can offer from coming out to my family as trans/crossdressing:
First of all, I had a feeling that my family would be pretty supportive. They are all pretty socially liberal and generally cool with LGBTQ things, but you never know when it's you and not just a group as a whole. So...while I did come out to them, I didn't come out to them until I was partway through college, had come out to my partner (who is still my partner now!), and had really reached a place where I was comfortable with myself.
For me I came out via email. I know it's a little impersonal, but I wrote a really thought out, long, and detailed email about sharing that particular part of me to them. I felt like it would give them the most space to respond as they needed/wanted. Their response was pretty much "we love you no matter what, but let's talk about this more."
So we took the conversation from there, talked on the phone, talked a bit in person the next time I had time to spend with them and it all went really well.
Which, unfortunately may not work for everyone...
But, I would say that giving them the space to process things, and then formulate a good set of questions, at least for my parents, helped out a lot. Just springing it on them in a conversation might have made it more uncomfortable for all involved. But no matter what I would say, know yourself, be confident that you are happy, healthy, and stable with who you are and want to be, and present it to your parents/family as your true self. If they truly love you they will understand. And make sure to have a good support network if things are a little rough. Most family can come around given time, but no matter what your family is like coming out can be a difficult process.
Hope for your sake it's not, my family was/is awesome.