Someone was asking me the other day about which of several cameras to buy to improve their photography. The typical photography enthusiast's response to that question is that the camera doesn't matter, and it's the stock response because it's true. However, I'm not immune to a bit of gadget lust so I'll always offer some recommendation if asked.
However, one of the simplest tips about improving one's photography is one I learned from the filmmaking, and it's a simple one that takes no skill to understand or learn. It's a concept that everyone who's ever watched a lot of movies knows, even if unconsciously.
Take photos where your subjects aren't looking directly into the lens.
In the movies, looking into the camera is known as breaking the fourth wall. It takes many actors years of practice to both be aware of where the camera is yet resist the temptation to let it affect their performance. In one student film I worked on, one actor constantly made the mistake of either glancing at camera or actively avoiding the camera with his gaze, ruining multiple takes.
[Most people recognize bad acting, but few understand just how hard it is to be an actor. I had to take an acting class in film school even though I was in the directing program, and it was one of the most frightening and uncomfortable things I've ever done, and it gave me an appreciation for actors that will last until I'm six feet under.]
Occasionally a director will break the fourth wall intentionally, but in the vast majority of narrative movies, the actors never look at the camera. Not once. To do so would break the fictive dream.
The reason this tip works is that photos are stories, and whenever your subject looks into the lens, the story is almost always, “Someone posed for a photo at this place.” It's a story, to be sure, just not an interesting one. What's more, it draws attention to the invisible photographer, too, since the subjects are responding to a camera being held by a person.
The vast majority of photos I see of people on Instagram or Facebook are of people, and of those, the vast majority feature those people looking into the camera. Selfies, posed group photos. They lack, for the most part, drama. They function as visual check-ins. Looking through a bunch of those in a news feed is like scanning a newspaper column which reads, “So and so were here. So and so were there. She was there. They were there.”
The moment your subject looks off camera, suddenly you are a photojournalist. For the viewer, it's as if they are transported to that place, and it puts them in a different state of engagement with the photo, a state of awakening. Suddenly they examine the body language and the arrangement of subjects within the scene (the mise en scène) to try to understand what is happening, just as viewers do when they watch TV and movies. Because the subject isn't looking into camera, the viewer doesn't read the body language as a pose, they read it as natural and thus more honest, worth deeper scrutiny.
As with most tips and rules, this one is not universal. Sometimes a gaze into camera is disarming, makes the viewer complicit, catches them in a moment of voyeurism. Sometimes you really do just want the subject gazing into the lens, as in much of portraiture. And sometimes the story you want to tell really is that some people were in a place together.
But if you're a beginning photographer and want to improve, that's my favorite tip because most photographers who are starting out take lots of pictures of people. At the next wedding or night out, try to shoot all your photos this way. It will force you to work a bit harder because when people pose for a head-on portrait the shooting angles are quite limited, but when you're photographing people who aren't looking at camera you can shoot them from almost any angle. It will cost you nothing.