One interesting question always to ask is what happens they your characters die, or when an important object is destroyed.
This CAN change everything, The best example of this is Ned Stark, his dying made everything much more interesting then if he had lived. Never forget that a book can be sad, or depressing and still be good. It can not be boring and be good.
I am not saying you should kill characters just as a cheap way to make your book interesting. However it often will not occur to you because you have so much invested in them. You should think about how you characters would/should die, even just as an exercise.
For example, Spock in Wrath of Khan dies in a way only he would. It made the movie much better then if they had found some easy way out, it gave the movie a weight that it would otherwise not have had.