Before you start selecting the color range in PS, you should make PS adjustments. For example, go to Image > Adjustments > Curves and bend the line in different ways to get the right lighting you want. You can also try changing the brightness/contrast and levels. This is especially helpful if the original photo is too dark or too bright. To view what it would look like to see if it is a good photo, open your photo in Photoshop and go to Select > Color Range and choose shadows. Copy the selection, make a new layer, and paste it. Do the same thing but choose midtones into a new layer. Then hide the original layer and you will see what it would look like when you use it for this assignment. The photo on the right is an example of the merged shadow & midtone layers.
It may be helpful to watch the first three minutes of the video tutorial which explains it in more details. Here are the Thousand Words' directions you will be completing in class.
If you read this late and don't bring a photo, that's okay, you can just use your signature photo but it may not turn out as good because of the lack of contrast lighting.
Before you use your photo, use the Adjustments > Curves like the image below to bring out the darks and whites.