Always use a custom alias. Adding a meaningful URI (clk.im/Join) will help users get a better understanding of whats waiting for them on the other side of the click.
Provide an intro. It makes no sense to spam the internet with your links hoping that someone will just magically click on your link. Add a few words before the link to get people to understand the context of why you think this link is valuable and relevant to them.
Some things are all about timing. There are many great posts about whats the best time to share content on each network to get the best engagement. We recommend you read a few to get a better sense of the optimal sharing time.
When in doubt – Test! A/B testing different link variations on a small audience will give you great insight into what works better. It may be that an alias such as clk.im/Join will work better than clk.im/SignUp. The only way to be sure is test!
Know your audience. Use different call to actions and links for different audiences. Don’t assume that your Facebook fans will behave like your Instagram followers or YouTube subscribers. Treat each audience as its own unique identity.