URL shortening is a nice way to earn money if you frequently share URLs with large audience. You can shrink your URL before posting it to social media, blogs or websites so that you will earn money for each user who visits the page using your short URL. This is effective when you share your URL among large audience like in a facebook page with large number of users, or on twitter with large number of followers.
Ad Fly is a free website shrinking tool that pays you money for each short URL viewed by the user. Ad Fly shows a banner to the user who clicks the ad for 5 seconds. After that, the user is prompted to the desired page. You can register in adf.ly for free and start shrinking your URL. Ad Fly shrinked URL looks like http://adf.ly/PvdbO (shrinked URL of this page). adf.ly will pay you via paypal with minimum payout balance 5$.