The most effective photographers are able to get their pictures to talk to the viewer.
Peter Hurley does this with head shots. Guy Tal does this with landscapes. Michael Reichmann does this with his own brand of street photography. The best images permit the viewer to become part of the conversation going on between the photographer and the subject.
Look at the best images in any photographic genre -- including food, fashion, architecture, weddings, product shots -- the photographer and the subject are talking to one another and the voices of both are present. The viewer listens in. Sometimes the conversation is so engaging it becomes three-way and the viewer actively joins it.
In most cases this conversation is not explicitly verbal. It's implied. Documentary and journalistic photography make it more direct and tranparent. Nowhere is this more so than in the work of Chris Arnade, who supports his art with a day job as a banker. Arnade has been photographing addicts in the Bronx, and permitting them to speak to the viewer in brief but wrenching statements.
I learned about Arnade's work in Chase Jarvis's blog. Link to it here. You can also see more images and read more stories at Arnade's Flickr page.