Choose a color temperature that suits your room. "Warm White" or "Soft White" give out a light that's similar to that of an old-style lightbulb - slightly yellow in tone. These would be great for rooms where you want to maintain a cozy environment. On the other hand, "Cool White," or "Daylight" bulbs give off a cooler, bluer tone - ideal for task lighting.
Choose the correct "lumen" rating to make sure it matches the wattage of your old bulb. The higher the lumen, the more light you get. For example, a 40-watt incandescent bulb gives off up to 450 lumens, a 60-watt bulb gives off up to 900 lumens and a 100-watt bulb gives off up to 1,600 lumens. You'll notice that energy-efficient bulbs require fewer watts to produce the same amount of light as an old-style bulb.
If you want to use an energy-efficient bulb with a dimmer or three-way switch, make sure it is designed for that use. And if you want to use your light in a recessed fixture, choose one specially designed for that situation.