I am one of those people who gets heavily into world-building for my fantasy writing. I find I really enjoy it (*cough* history major*cough*), even though it can take enormous effort. For someone who hasn't done it before and is feeling anxious, I suggest starting out with Patricia Wrede's world-building questions, found here: http://www.sfwa.org/2009/08/fantasy-wor ... questions/
I found that I wanted to go beyond these questions, so I dug out a doorstopper 2-volume book set called A Social History of Ancient Ireland. I has used it for research in college and had been very impressed with the variety of topics, even if some of the actual information had proven erroneous since its publication. I sat down with a pad and pen and noted every topic the volumes covered. I then combined these questions with Patricia Wrede's question to come up with a massive
world-building template. I will skip revealing how many pages of questions I have, so as not to frighten any novice world-builders. I will say, however, that I find it incredibly
useful for generating plots and story ideas. I also feel less anxious that, in the course of writing, I might accidentally toss in some detail that just would not fit with a particular culture or landscape.
Of course, as mentioned already, it is very important to recognize that the vast majority of the information should not end up in a novel or short story. It will provide context for the decisions the writer makes. Beware of adding more just because the info is so darn cool. The reader will spot this every time.