As with many quilt blocks (but by no means all), Snowball is descriptive of how the block looks, and it's simple to do--when you know the secret of corner triangles. It is often used as an alternate block, but it can also be used "on its own."
For a 12" block you will need:
(1) 12-1/2" square light
(4) 4-1/2" squares dark
Using a white, silver or yellow pencil draw a diagonal line from corner to corner on the wrong side of each dark square.
Place a dark square (right sides together) in one corner of the light square and sew on the drawn line. Trim the excess, approx. 1/4" from the seam. Fold back the triangle and press. Repeat with the remainder of the squares, and corners of the light square.
You might use Snowball to showcase lovely, large prints; the corners would help to separate and feature the print. Or, the Snowball block is a wonderful alternate block, and can be effectively used with nine-patch grid blocks (those that are 3 x 3 arrangement of units), such as the Nine-Patch, Friendship Star, or Monkey Wrench.
You can change the size of the dark squares to suit your needs. For example, you could use it for a photo quilt, using the corners as a frame, or accent piece--in which case you might want the corners to be smaller.
Here's the Snowball used to actually act as a snowball, in a quilt I designed a few years ago. (Mittens are a favorite winter motif for me...)