It's a beautifully formed word, isn't it? Playing on the lips like a kiss. It's also life and death for speculative fiction. I was reviewing some handouts I got from Terry Dowling at a spec fic writing course many moons ago. Terry advocates a huge amount of thought should go into building imagined worlds. Some might say he takes it to an almost ridiculous degree, but you only need to read one of Terry's stories to feel the reality of the worlds he creates at a granular level. So I'm firmly with him on this.
As writers, we think about a lot of these things in broad terms. You focus on the immediate detail to support plot advancement. But if your character is a loner you may not worry about kinship structures or how family units function in a particular society, what the prevailing view is on monogamy, polygamy, hetero or same sex couplings, associated mores, taboos, how property is invested, and passed on. But all of those things, if you really took the time to sit down and map them out, could provide some interesting local colour for your story. That's nice. But even more importantly, they could open up a whole raft of previously unconsidered plot twists, complications and so on that take your story to the next level.
Terry has a list of 14 major headings to think about in world building. Some are obvious, like religion, to the not so obvious like the preferred sport and its origins. I won't go into the whole list here because it's not mine. But 10 or 15 minutes leafing through a newspaper will give you an idea of the sort of things that are deemed 'interesting' or 'essential' to our society. It's only a short thought experiment from there to constructing a radically different set of fundamental societal keystones. Then the fun can begin.
Oh, if you can get a hold of it, I also recommend Worldbuilding by Stephen L Gillet. That looks more at the physics that form and act upon planetary bodies. Another way to add that all important verisimilitude.