If it's one large character or character face, the eyes are the most important feature to draw in your viewer. For the Wise Ancient Tree I put in the darkest-darks in large patches around his eyes, so they wouldn't let lost in the rest of his detailed face.
Some of the elements around the professor also direct your eye and literally point towards him, for example the white bill of the woodpecker pointing in his direction, echoed around him by the bear's snout, the branch on the log and other animals all pointed towards him.
(Click on these images to see them better...they will grow!)
Try to find ways to frame your character with shapes that will direct the eye towards one central focal point. In this drawing, elements on the Professor's left (the test tube and weighing apparatus) lean in straight and diagonal while elements on the right repeat a curved shape (in the feather, microscope, his hair and shoulder), all leading the eye to the area in the drawing where his eye stares intensely at his scientific work, which is the whole point of this particular moment in the story.
Simply put, ask yourself what one thing this drawing (or shot) needs to communicate to your audience about the story you are telling, and find a way to draw your viewer's eye to that one single point that communicates this with the most clarity.
I hope that helps!