Choose any shoebox.
Cut out the top, left, and right sides with an exacto knife, only keeping the frame in tact.
Your box should look like this when you're done cutting out the sides.
Tape white tissue paper to the frame of the box to cover up the square holes you just cut out. (I folded mine so it was thicker by 3 layers. The more layers you have the more diffused your light will be.)
Cut a piece of white poster board to fit inside the box, but make it slightly longer than the length of the box. Fit it into the top of the back of the box like so.
Fold the remainder over the bottom of the box and tape it down.
Next, adjust a light source at any side of the box. I use a Trademark UV light lamp, which was about $25 on eBay.
Now you are ready to take pictures! Adjust your object within the box and snap away!
Here are two pictures, one without a light box (left) and one using a light box (right).
You can see how in the picture without the light box, there is a huge glare on the nails. With the light box, it's easier to see the shapes of the glitter and the depth of the polish. The photo using the light box also has softer shadows, a sign that diffused lighting was used.
You can use light boxes for photographing other products as well...
This is the best way to photograph something where you don't want the background to distract the audience.
I hope this tutorial was helpful for anyone looking to make a light box!