Live the life you want to write about. I don't mean go robs banks if you want to write about a bank robber. I do mean get into your life, into the world in general, as deeply as you desire and are able. And the further you are outside your comfort zone, the better it will probably be when you start your world-building. Nobody would have cared about Anna Karenina if she were just a happily married woman, except maybe her husband and family. But throw her into darkness, and all eyes are upon her. I doubt Tolstoy could ever have created someone like that by staying on the farm.