If the first question is what do you want a visitor to do, the second is what do you want a visitor to your online community to know?
Do you want them to know this site is unique or special in some way? If so the site has to offer something unique or different from any other community in its field. This will require custom development. Place it prominently.
Do you want them to know this is a popular place to hang out? If so, show lots of activity taking place, display the number of members participating, and highlight any other success metrics.
Do you want them to know they could build a powerful reputation here? Show the people who have built a powerful reputation in the community. Feature them highly.
Do you want them to know to know this is a private, exclusive, or even secret community? If so, show nothing. They have to join first.
Do you want them to know they shouldn’t be scared or feel they have to be an expert to participate? Place beginner-level topics and a newcomer option on the homepage.
Do you want them to know the guidelines for participating? Then prominently display the guidelines.
Do you want them to know the latest news or most popular topics? If so, feature these prominently (Sonos does this well).
The problem is most platforms aren’t sure what they want people to know. Unable to decide they go with most of the above. Don’t do this.
If the call to action (CTA) is the single action you drive everyone to take, everything else tackles the emotion that gets them to take that action. Make a clear choice what emotion will drive the action you want. This should be linked to your online community’s strategy and where your community lies within the online community lifecycle.
What you want the audience to know will change over time.