Culture is, obviously, one of the key components of creating any fictitious world.
One often-overlooked aspect of world-building, unless your story specifically involves deities and religious beliefs in some way, is the matter of religion...or what your world believes. Maybe the gods are directly involved, maybe they are distant and uncaring about their creation, but most cultures have begun with some sort of higher power(s) as creators and/or ways of explaining natural phenomena in their worlds. Even in technologically advanced societies, where the inhabitants have evolved to a point of explaining everything with science, are like to have had roots in some sort of religious environment and there are always people in search of a higher power, a reason for existence, something to believe in.
One of the best resources I ever found for creating religions is a D & D manual designed for priest characters, which includes an entire section on religions. I haven't found those pages online yet, but I have collected a few other resources over the years. Some things to consider are how beliefs influence culture and vice versa.
Not all of us are brave enough to even consider developing a language for our worlds...but for those interest in giving it a go, here are some links with useful guidelines and tips: