How do you "learn" to be selfish

Had a conversation recently with Moosh about this. And since then I've been pondering it. How does one learn to be selfish? I've never been good at it. So I put this out to you guys. How do you do it? How after a lifetime of putting everyone else first, do you put yourself first? How do you make that hard decision that will hurt others, but is the right one for you? Is it better to make all the plans and have all the dominoes in place before you do, or is it better to do it and then let them figure out all the dominoes and where they go? Are small steps better, going to the gym, not paying their bills, not doing the things you'd normally do then say the big one? How do you even know where to start? I know I have to do something, because this is literally killing me. Muppet screaming and arm waving isn't far off.....