Photograph the Eye Close Up

Have you ever seen a closeup of someone's iris? It is a fascinating subject to photograph.

Steps

Know what you are going for. Do you want just the iris and the pupil? Maybe you want the whole eye. If you are going to do the whole eye, you might want to put some eye makeup on. Or not.
Choose a strong continuous light source, or try it by a window on a nice sunny day. You could use a flash, but it can be a bit 'bright' for your poor subject.
Create a comfortable place for your subject to sit. A table can be useful to prop up your subject's head to eliminate any movement.
Make sure that the sensor (or film) is perpendicular to the eye.
Have your subject look right at you.
Put your camera on manual focus and aim it at the iris.
Be sure that your aperture is not open wider than about F8. This will allow you to get in enough light and also have enough depth of field.
Set the shutter speed to fast. This prevents blur from camera or subject movement.
Be particularly aware of the reflections that are going to show up in the eyeball when shooting.

Just before you click the shutter, ask them to blink to reduce the likelihood that they will blink while you are taking the picture.
Try to keep the setting short and/or allow your subject frequent breaks. The longer they try to keep their eye open, the more it will water.
Try to keep the pupil as small as you can, unless you want a large pupil. Most people are trying to see as much as they can of the iris. If the pupil is too large, then the picture is usually not as interesting.

Take Macro Photographs Without a Macro Lens or the Determine Your Macro Magnification
Tripod
Continuous light source or Increase the Amount of Natural Light in Your Home