Summarize this article:

Make it big, but not very thick. Rub that on your smudged finger. Start at the inside corners of your eyes and work the mark down and out slightly. Start from the outside edge down toward the first mark if you want a more extreme effect, or for darker lighting.

Summary:
Get a black marker; preferably washable. Draw a rather large smudge on one of your fingers. Take another finger on the opposite hand. Apply the marker to below your eyes carefully. Add a much lighter bit.