By far, the safest way to view the transit is to construct a so-called pinhole camera. A pinhole, or small opening, is used to form an image of the sun on a screen that is placed about three feet behind the opening. [Video: How to Make a Solar Eclipse Viewer]
Binoculars or a small telescope mounted on a tripod can also be used to project a magnified image of the sun onto a white card. Just be sure not to look through the binoculars or telescope when they are pointed directly at the sun! Venus should appear as a distinct, albeit tiny dot on the projected image.
A variation of the pinhole theme is the "pinhole mirror." To make one, cover a pocket mirror with a piece of paper that has a quarter-inch hole punched in it. Open a sun-facing window and place the covered mirror on the sunlit sill so that it reflects a disk of light onto the far wall inside.
The disk of light is an image of the sun's face. The farther away from the wall you place it the better; the image will be only one inch across for every 9 feet (2.7 meters) from the mirror. Modeling clay works well to hold the mirror in place.
Experiment with different-size holes in the paper. Again, a large hole makes the image bright, but fuzzy, and a small one makes it dim but sharp. Darken the room as much as possible for the best effect. Be sure to try this out beforehand to make sure the mirror's optical quality is good enough to project a clean, round image. Of course, don't let anyone look at the sun in the mirror.