1/
The subject must be static, no movement must occur in the subject during the 2 exposures.

2/
A good depth of field adds greatly to the 3D effect.

3/
After you have taken the first photo the camera is moved to the right 1/30th of
the distance from the camera to the subject. In other words if your nearest
subject is, for example, 30 inches away from the front of your camera lens,
 move the camera 1 inch to the right for the 2nd photo.

4/
When you move the camera to the right for the 2nd shot, it is very important that
the camera remains horizontal. Do not tilt the camera in any way; you can do this with a hand held camera for wide shots,
but for a better result that gives you more control over depth of field etc.,  you can make or buy a slide bar that fits onto your tripod - this can be made out of wood or metal.
A slide bar gives the camera a flat surface to sit on, and enables much better accuracy when sliding your camera over to the right
for the 1/30th separation.

5/
When you look through your viewfinder for your left shot (1st photo)
you need to see slightly more of the right side of your closest subject, and conversely, when you look through your viewfinder for the right shot (2nd photo)
you need to see slightly more of the left side of your closest subject.
This creates a stereo window where everything is slightly "back" inside the window. You can have things coming out of the screen
but this works best if the subject does not touch the sides of the picture frame, so producing what we call a floating edge.

6/
When using a flash for lighting, do not have the flash attached to the camera as
the flash must not move between the 2 shots.

If you follow these rules, there's no reason why you won't get stunning 3D results, good luck.

VIEWING YOUR 3D RESULTS.

If you have processed your pictures as prints, you can buy a Loreo 3D print viewer (for viewing side by side small prints),
or a View magic 3D viewer, (for viewing larger format prints, above and below) try your local photographic supplier, or you can order from Stereo World in the USA.

If you have shot with slide film, you can buy a couple of those hand held 35mm  viewers that you point to the
light and bring the eye piece to your eye. stick the two together so that the centre join remains flexible to allow
for variations in peoples eye separation. put your left slide in the left viewer, the right slide in the right viewer
and then be amazed.