The easier you make it for readers to contribute, the more likely they'll get involved in your community. Using "calls to action" can accomplish this by telling them what they can do on each page, and how to do it.

Here are some general tips:

• Keep calls to action short and to the point.

• Use active verbs: "Contribute, Add, Build, Create" etc.

• Encourage conversation around a topic by pointing readers to the "Comments" section. (Even better, create a link to it so people can add a comment with just one click.)
  

• Try putting calls to action at the top or middle of the page, not always at the bottom (some people may not read that far!)

• Keep the formatting for calls to action consistent throughout your wiki--users will hopefully start to recognize them as "action points" on every page. (on wikiFido we use a graphic paw, but consistent formatting with a bullet, for example, works just as well.)
  

• Apply the same rules for style and formatting to your calls to action (avoid all caps, large fonts, multiple formatting styles, etc).