Make sure you read the terms and conditions of each url shortening site, since some methods posted below are not allowed by certain adnetworks.
If you want to play safe you can always use the coinhive url shortener since they allow every site.
1. You can pay people to visit.
The most obvious way of doing this would be by making a faucet. There are a few very simply ways to make one for free, and those support url shortening services. Pay every user a small amount of cryptocurrency for every visit and when the reward is high enough they will come back.
Other options would be paying people on the marketplace here, but that is not viable with most earning rates.
2. Promote a download/project
People love free, and they love free downloads. Ever found yourself searching for a file and all you found were urlshorteners? Exactly, those people make money from the clicks they get on people searching for downloads.
You can do this with a Youtube channel, Facebook page or website. I recommend you use a website and host the url shorteners there since Facebook and Youtube tend to blacklist url shorteners.
There are cheap offers available in the webhosting section on this forum.
These are the most obvious choices, since most people dont visit url shorteners without getting rewarded in the end. May it be free cryptocurrency, or the download, textfile etc.
Take a look at who uses url shorteners and learn from those people on where to put url shorteners, and what url shorteners to use.
For faucets it is obvious, just look at other faucets that use url shorteners and been in business for a while.
Other kind of sites you might need to search a bit harder.
Promoting url shorteners is certainly possible, but it can be hard if you dont have an audience at your disposal to throw at the url shorteners.