These guidelines are to help all of us make UI reviews as straight-forward as possible.
= What is this page trying to tell me =
Although it may be out of the scope of the current branch that you are working on, it is always worthwhile getting the big-picture...
Create a screenshot
The UI review process will be much faster if the reviewer can view your change without having to merge and run your branch. Sometimes this can be as simple as attaching screenshots to the bug (this also allows other interested people to comment).
If your UI change involves a behaviour, consider creating a brief screen-cast using gtkRecordMyDesktop.