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.)

In ChangeLog files, it is best to use ways of identifying revisions
that are not dependent on a particular version control system.  (At
time of writing Emacs has just moved to its fourth VCS and another
move in the future is not impossible.)  An excellent way to identify
commits is by quoting their summary line.  Another is with an action
stamp - an RFC3339 date followed by ! followed by the committer's
email - for example, "2014-01-16T05:43:35Z!esr@thyrsus.com". Often,
"my previous commit" will suffice.