For most home applications, 1 to 2 watts per square foot is sufficient. For a work area where you need a lot of light, such as a workbench or sewing room, some people prefer to go as high as 3 watts per square foot.
There may be local regulations limiting the wattage per square foot. These are more commonly given for businesses, but some areas have restrictions for homeowners as well. Check for such restrictions before you install fluorescent lights.
In addition to measuring watts, also take note of the lumens various types of fluorescent bulbs offer. Lumens are a measure of the power of light as perceived by the human eye. Many bulbs provide information about their efficacy in lumens per watt. This enables you to get brighter light with the same wattage.
CRI, or Color Rendering Index, is another measure of how humans perceive light from fluorescent bulbs. A higher CRI means colors look closer to how they appear in daylight, but some people also perceive higher CRI bulbs as making a room dimmer. This is another way you can vary the brightness without manipulating the watts per square foot.