The most important tip to follow when using mirror reflections for art or abstract images is to make sure the mirrors are clean. Blotches, spots, or a streak on a mirror is a great way to cause an image to loose quality.
Do not use filters when working with reflections. A common reason people choose to use a filter is to reduce the glares and reflections that appear in an image. Therefore, a filter would distort the image and cause it to look dull when working with mirrors.