Turn off the light. If the bulb is in a lamp, unplug the lamp. If it's in a ceiling light, shut off the power to that part of the home at the breaker box.
Unscrew the bulb from the light fixture socket.
Shine a flashlight on the light fixture housing. Locate the small metal tab in the bottom of the light fixture housing. Insert a flathead screwdriver under the tab and bend the tab upward slightly.
Look for a round plug in the light fixture housing for a fluorescent bulb. This is the starter.
Wiggle the starter to see if it's loose. If it is, press it back into place until you hear a click. This should fix the flickering. If the starter isn't loose and the bulb still flickers, then the starter is faulty. Remove the starter by twisting it out of its socket.
Click a new light fixture starter into place. Make sure that it has the same amp rating as the old one. Replace the bulb.