Overview screens have certain common elements that let the user know what it is they're looking at, and how they're expected to use the screen. It's helpful to know how people look at a screen when they see it for the first time. Studies by groups such as Neilson show that most western people follow a sort of F shaped pattern when looking at the screen for the first time. Starting in the top-left corner, their eyes track right and downwards, as shown in this diagram:
This means that when designing an overview screen, the most important information should be at the top of the screen, with the second most important information to its right, and as you work down the screen, the information becomes less important. The preceding diagram uses a graph at the top of its screen; this is also an important element: favor using graphics and indicators over raw numbers where it's applicable. A user can get a much quicker overview from a graph than they can from a table of...