There's no much secret here but I'll give some Ideas

Like our honeys said, Yeah, I think that create a new count with your "new identity" is one of the first things to do. Off course you can just change your actual count to reflect you from now on, but I don't like the idea. You can also keep the old count, and at the same time start a new one, in this way you can keep the two counts with two personalities each (I personally don't like much of this idea). If you do to keep the two accounts, you can keep you relationships relatively safe and choose who you want to know the another you.
Whatever you choose before, with your new account, you can select who you want to still be friend. You can invite person by person to your new account, you can do a post inviting whatever who wants to still be you friend, you can do both. Just be prepared for the possible reactions and even rejections. for example, I have, in my facebook, a lot of Christian friends, and the trans-phobia is very present, so I can't expect much acceptance from them, they are very likely to be lost friends. I don't think that I would receive aggression, but you must be prepared. (I still have to get out of the closet, just to mention).
Well, after that, the rest of you online presence is just part of "be yourself", if you like to post cute things, do so, if you like to post articles, do too, post whatever you like to. It's a new presentation of you to the online social media, would be rather boring if you try to be someone that you are not in your new account. Thinking about that, now I realize why my facebook is so boring