This story shows you where to place windows.
A kitchen window is typically placed higher than the top of a countertop's backsplash -- usually 42 inches. In living and dining rooms and perhaps in some bedrooms, you can increase the view by installing windows with the bottom as low as 12 inches above the floor. Placing the bottom of the window about 36 inches above the floor allows wall space to accommodate dressers and other furniture.
For aesthetic and practical reasons (that is, to accommodate the width of a structural header over the window), it's usually a good idea to keep the top of a window at least 16 inches below the ceiling.
In a dining area it is common to have a windowsill at the typical height for a table -- about 30 inches.
When possible orient windows to make the best use of natural light and weather. Weather tends to move from west to east in the United States, and windows placed on east or west walls gain or lose more heat than those facing north or south. A southern exposure will receive plenty of sun, while a northern exposure will receive little direct light. Of course east-facing windows receive morning light and west-facing windows receive sunlight in the afternoon. Consider prevailing winds too.