Composition: Rule of Thirds
You've probably heard of the Rule of Thirds. The idea that having a key element of an image (such as the horizon line for example) one third of the way into the picture makes it more visually appealing. It's only a guide, and thought to be an approximation of the 'golden ratio'.
Here's a more lengthy explanation on Ultimate Photo Tips: Photography Rule of Thirds
The Histogram, Shadows and Highlights
There's an expression, "Expose for the highlights" or 'Expose to the right". It basically means to get the highlights in the image right as a first priority, allowing the highlights to be bright without being blown out (i.e. allowing the brightest parts of the image to be close to, but not absolute, white). It doesn't always hold true (you might choose to over-expose the sky for example in order to correctly expose the face in a portrait). Here's Adorama TV with more detail and how to use the Histogram in your camera and editing software:
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Portraits & Headshots
Along with lines ('leading lines') and high contrast, our eyes our naturally drawn to the brightest parts of an image. You might find that your subject, where you want your viewer's eyes to go to, is too dark or there's a bright distractions elsewhere in the image. Most editing software allows you to selectively dodge (lighten) or burn (darken) a specific area of an image using either a brush or defined area (linear or radial filter in Lightroom). Here's a tutorial for Lightroom but the tools are very similar in other software:
Workflow is h
Experiment with a photo app or two, whether that's on a laptop, phone or tablet. Pick and image and try different crops. See if you can draw the viewers eye more strongly to the subject of the image.
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