"The camera is an instrument that teaches people how to see without a camera."
Dorothea Lange
Of all the things people who are new to photography must master, training the eye might be the most challenging. Even seasoned photographers have days when they're just not seeing much. Especially if fatigued, it's tough to be creative.
It takes time to learn to see like a photographer. Once you do, though, you'll never look at things in the same way. This might drive your non-photographer friends and/or relatives a little crazy. My husband has asked me more than once, "Can't you look at something without thinking about how you'd shoot it?"
That's such a silly question. Of course not!
But how exactly does one go about developing photographer's vision?
Practice Mindfulness
The world is full of distractions (one of the worst offenders, your phone, is probably next to you right now).
Our environments are often noisy. Busy. We routinely multitask.
Our brains often "tune out" certain things because our attention is focused elsewhere. This phenomenon is referred to as inattentional blindness. When this occurs, we might be unaware of things that are right in front of us, particularly if we've seen them many times before.
Step one, then, it to learn to quiet your mind, fully engage with your surroundings and focus on the here and now.
Put the phone away. Forget about the project deadline back at the office. Or the grocery list. Or where you're going to have dinner.
Be present.
Slow Down
As Simon and Garfunkel once sang, "Slow down, you move too fast."
We miss a lot of things because we don't give ourselves time to notice them.
Too often, we rush to get to the end of the trail. We hurry to take our cameras out. Once we make the photo, the camera quickly goes back into the bag. We scramble to move on.
Slow down. Linger. Take your time.
If something catches your eye, stop and have a closer look. Don't be rigid, either with your schedule or where you're wandering. Give yourself a chance to connect more deeply with the location and/or subject.
Avoid the impulse to pack up right away. After you've released the shutter, have another look. Have you thoroughly explored the subject? What if you change the orientation of the camera? Swap lenses? Shift your position? The second photo you make might be better than the first.
Doing these things means you might not cover as much ground as you originally anticipated. So what?
Use All Five Senses
Why should your eyes do the heavy lifting all by themselves?
What do you hear? What do you feel? What do you smell?
Paying attention to what your other senses are telling you will improve your ability to observe.
It Doesn't Have To Be Literal
Use your imagination.
Avoid labeling things; this tends to limit your thinking. Fir trees might be triangles. Rocks are ovals. Buildings, rectangles. And so on. Consider how these shapes relate to one another.
Change your perspective.
Experiment.
The following photograph is an example of a whimsical interpretation of an object. I made this at Marina City in Chicago: it's one of the twin Marina Towers. Shooting at an angle, I saw an open book: the center line is the spine. There is no rule that says you cannot represent subject matter in an unconventional way.

Take the Blinders Off
Remember to turn around. Look up. Look down. The photograph may not be in front of you, where you expected to see it.

I made this photo at Oxbow Bend in Grand Teton National Park. If you're familiar with the Bend, you know most people who stop by are (understandably) focused on Mount Moran and the northern Teton Range, which tower over the landscape 180 degrees from this scene.
On this evening, though the weather was lovely, there wasn't anything particularly interesting going on in the sky over the mountains. Watching the sun go down behind them would be nice to experience, but that's about it.
While the sun dipped lower, I kept an eye on what was happening behind my shoulder.
A stand of aspen trees, brightly lit from the last rays of the setting sun, appeared especially vibrant when contrasted with the dark greens of the surrounding conifers and the rest of the landscape already in shade. You can see that the neighboring aspens to the right, which are actually just as colorful, aren't noticeable at all because they're unlit.
Most of the time these aspens standing near the bend of the river are somewhat unremarkable, but on this evening with that lighting, a few lingering clouds, and the mirror-like reflection enhancing the scene, they were begging to be noticed.
Take a Walk Without Your Camera
When you first arrive on location, sometimes exploring without your gear can be beneficial - especially if the place is new to you. It's a good opportunity to get in sync with the area. Listen to what it's trying to say; it will help guide you to photographs if you let it.
Be aware of light: its color temperature, its characteristics, and its source. Study shadows. Look at the way things are arranged. Find patterns. Make note of potential subject matter. Compose photographs in your mind.
These often turn out to be extremely useful scouting excursions, in more ways than one.
Even when you're unable to shoot for a while, don't let your eyes get lazy. Practice intentional observation. You can do it anytime and anywhere.
The more you look, the more you see.