One of the most important skills a new photographer can develop is the ability to see light. For me, there was a progression towards this goal.
First, I saw interesting things - subjects for me to photograph. Then I placed a subject in the frame, moving it onto a rule-of-thirds line, into the foreground/background - in other words, I focused on composition. Now, I've started to see light; where the shadows fall, the bright parts of the scene, that sort of thing.
Light makes all the difference
Let's look at a sample case. I love to photograph the Clark Bridge spanning the Mississippi River near my home. I visit often at all times of the day and night to photograph this bridge.
Notice the light at 5:30 am on a spring morning spilling over the bridge. It creates a rainbow effect in the sunbeams and picks out details of the bridge. Without the light, this would be an ok photo. There's a leading line and the interesting part of the bridge is on the rule-of-thirds line. But composition isn't enough. This photo is really only interesting because of the light.
Earlier in the month, I'd tried to photograph the concrete pillars under the bridge at 10am. I'm not sure why, I must have thought there was something interesting. But the photo wasn't anything special. It went straight to the cutting room floor (metaphorically).
But I tried again a couple of weeks later, this time at 5:40 am. Same bridge, same vantage point - different time of day. Notice that the light picks out the top and left edges of the concrete pillars. That's where my eye goes, not on the concrete itself - just the shape.
There is also a beam of light coming in at the far end giving the photo a light-at-the-end-of-the-tunnel effect which provides focus.
Also note the reflections which are visible in the water elongating the pillars and setting up a leading line into the photograph. This effect is only visible when the light is coming in at the oblique angle of sunrise. Reflections had disappeared by 10am.
This was the first time that I really understood how light could change something ordinary into something extraordinary. This photo has recently taken grand prize in a competition about the Mississippi River. Of all the beautiful parts of the river from Minnesota to Louisiana, this one - of functional, foundational pillars - took the prize. It wasn't the subject that made this photo - it was the light.
Photographers talk lovingly about the "Golden Hour" - the time of day when the sun sinks low on the horizon casting light obliquely across the scene. It's not so much about when the photo is taken, it's about the light that happens at this time of the day.
Everything seems to take on a magical glow at golden hour, so check local sunrise & sunset times and plan to be out just after sunrise or just before sunset for the best light.
Light is sometimes most powerful when it's not there. Shadows can only be created when there's light - blocked by something. To create shadows, light comes in at an angle, so there won't be many shadows when the sun (or any light source) is directly overhead.
Shadows add depth to the image and sometimes play with reality - elongating shapes. Shadows emphasize the line or outline of an object or person which is why some of the best shadow photos are black and white. Black and white emphasizes line and shape over color. Shadows can create interesting patterns on an otherwise mundane image. Shadows can even be the subject of the photo.
Shadows add an element of repetition in the image. The shadow isn't quite the same as the subject, but it's similar in shape. And sometimes, shadows can create a leading line - guiding the eye to the subject.
So, don't forget to look around the subject and see the light - and the shadows. You can even be in the photograph - or at least your shadow can - if you want to be. Otherwise, make sure you're not standing with your back to the light!