Honestly, for me, once I accepted that I was poly, and told my husband, everything else has been incredibly easy. It took him a couple of months to process his emotions, and then I started looking to date. Within a month, I had been a couple of dates and met someone special. We've been together for six months with virtually no problems, other than there is never enough time, but I think that's an okay problem to have.
In terms of how I started, I told my husband that I was poly, that I was driving myself crazy trying to fit into a monogamous life and a monogamous relationship and that I hoped he accepted me for who I was. His first step was to accept me for what I was, and that I wasn't going to change. Then he decided that he'd rather love me and have me and have me be happy than force me to be miserable or have me leave him. And it has worked nearly flawlessly since then.
I still haven't told my parents or my brother, but I intend on doing so relatively soon.