What's a call to action? It's the reason a web page exists. The thing you want your reader to do next. This presentation provides 20 do's and don'ts, covering a range of graphical and editorial considerations.
You might not be looking to get your reader to 'buy now' but you should be wanting them to do something, even if it's just read another page.
While the range of tips here is wide, there's still plenty to be of interest to a content editor without access to design.
20 do's and don'ts for clickable calls to action - Hubspot presentation on Slideshare