One book that really helped me in discovering ideas for my world building is a book called Guns, Germs, and Steel by Neil Diamond. It was the required reading for the world building class I took at my university last semester. It presented a lot of explanations as to why Earth is the way it is now, and I took some of those explanations and applied it to my world, while I took others and bent them because there's magic in my world that would change the results.
I also find inspiration through reading about various cultures throughout Earth's history and taking aspects from them and molding them to fit within my own. I just look around Wikipedia or I browse National Geographic until something catches my attention.
I am fortunate that I live in an area with a large science fiction and fantasy community, so when I can, I attend the various cons and writing symposiums that are held around here. They have a lot of panels on world building and coming up with ideas. Try looking for similar events around you, if there are any, and try to attend. If you are a student, try looking for discount tickets too.
Finally, what helps the most is being able to find others to bounce your ideas off and perhaps they can give suggestions on how to make it even better. Of course, being part of this tribe is the perfect place for that.