Plot Problems

I am having difficulty developing the plots of the now seven book series. I have plots for books 1, 2, 6, and 7, but the middle three are proving difficult. I would like to see adventures into the lands of the other three races in addition to continuing the overall storyline. Several good ideas have come to mind while staring at several relatively blank notebook pages and a pile of note cards. Some of the ideas have even ended up on the cards!