@ Up in the Air
I find it helps to push through those "blocked moments" by trying to write whatever comes easiest at the time--don't worry about if it is actually any good or if it in sequential order, or if it will even fit into the story in the end. Just put words on the page until something usable DOES come out!
I am personally a big fan of world building. I have maps and charts and lists and sketches all over the place! It can be hard sometimes, though, feeling like I have to have every little detail hammered out in order to make it work. But I read an article recently that talked about focusing on a few main characteristics to build a foundation, and the rest of the details will either not even matter because they won't come up, or they'll pop up as you write. For me, I focus on geography (the map stuff); the economy--what would these people live like, rich/poor, what do they do for a living, and how does it effect their culture and values; how does this effect, in turn, my story and my character? how does it drive them or motivate them into the story and the climax? Does it make sense in the geographical setting? i.e. mountainous terrain would put more stock in hard work, but the character may be considered lazy, so she/he leaves to find a place in the world. The family probably wouldn't be rich, so it would make sense that she/he may come from more humble roots. This would come into play on his/her adventure, maybe coming across richer communities by the sea, different cultures. Etc.
I have often fallen in the rut of "waiting for inspiration". All the articles and books I've read, however, all say to try to write something every day--even if it sucks or it has nothing to do with the actual book project. Getting words flowing onto a page will help in itself. You can always throw it out or go back and edit it!
I really hope this helps you a little. Don't worry about being good or waiting for inspiration! Just write! The rest will come out eventually! This principal has helped me so much with my writing!
For tips on world building, try
this article.