Manual:Force preview

Force preview is JavaScript that prevents specified individuals or groups from saving a wiki page before they preview it at least once.

In order to use this code, insert it into your wiki's Mediawiki:Common.js page.

Note that this method is not foolproof. If a user disables JavaScript in their browser, they will not have preview forced on them. If you want to ensure that this policy is enforced, then you should look at Extension:ForcePreview.

For Mediawiki 1.14 or newer
The following will permit you to control who has preview mode forced on them. It permits you to set one or more user groups to bypass forced preview and save directly. In order to permit a user group, add the group name to the permittedGroups array as shown in the comments with the JavaScript code.

Older Versions
The below scripts are based on Marc Mongenet's script, from.

Force preview by wgUserGroups, requires a MW version >= 1.10
If you wish to provide exceptions to certain usergroups. Just change == (EQUAL TO) signs to != (NOT EQUAL TO) Common choices range from "user", "bureaucrat", "sysop" and more depending on your configuration.