|Moon over Los Angeles|
The first step is to go back through what I've written and look for gaps. Filling holes often provides the connections that make ideas link together. When this doesn't work, I often find it more productive to get away from the project temporarily. Basically, to get a good night's sleep. When I go back to the project the next day with a fresh, and sometimes, an empty mind, it is easier to see the big picture and not get hung up on the nitty gritty.
As far as my illustrations go, one of my techniques for getting unstuck is to lay them all out in order, either on the floor, or on a big table. That way I can see sequences and whether the pages flow from one to the next. I can also tell if I have a good mix of close-ups, medium shots, and panoramas. I can also check to see if I've been consistent with my colors and backgrounds.
And, in either case, it is always useful to take my project to my writers' group. It is amazing how an outside viewpoint can zero in on a problem section, that I, as the author or illustrator, am too close to see.