Emacs generally follows the GNU coding standards when it comes to ChangeLogs:
http://www.gnu.org/prep/standards/html_node/Change-Logs.html

One exception is that we still sometimes quote `like-this' (as the
standards used to recommend) rather than 'like-this' (as they do now),
because `...' is so widely used elsewhere in Emacs.
http://lists.gnu.org/archive/html/emacs-devel/2014-05/msg00514.html


If installing changes written by someone else, make the ChangeLog
entry in their name, not yours.


http://lists.gnu.org/archive/html/emacs-devel/2007-09/msg00793.html
  There is no need to make change log entries for files such as NEWS,
  MAINTAINERS, and FOR-RELEASE.
"There is no need" means you don't have to, but you can if you want to.


http://lists.gnu.org/archive/html/emacs-devel/2006-12/msg01135.html
  There is no need to indicate regeneration of files such as configure
  in ChangeLog.


http://lists.gnu.org/archive/html/emacs-devel/2008-11/msg00940.html
Preferred form for several entries with the same content:

   * help.el (view-lossage):
   * kmacro.el (kmacro-edit-lossage):
   * edmacro.el (edit-kbd-macro): Fix docstring, lossage is now 300 keys.

(Rather than anything involving "ditto" and suchlike.)