Composition in photography is almost exactly the same as composition in classical art. The only difference is an artist has full control of what they put down on canvas, however the photographer has little control of the scene. The limited control is exerted in the form of patience, waiting for the light to change, waiting for people to appear in certain positions, or changing where they stand with their own two feet.
Composition is the total sum of all of the elements in a subject and how they interact with each other. It is often confused with framing of the subject which it is not but framing does play a role.
Due to the intrinsic nature of art itself, there is no objective measure of what makes an image well composed. Images that are deemed terrible on one day can win international competitions on another. As mentioned on a previous page, a significant proportion of what we feel about an image is what emotions, if any, it evokes in us as individuals. A good photo is emotive, it raises questions and tells a story. It is about a subject rather than of a subject.
There are certain helpful rules that beginners can follow with regards to composition, but by no means are they hard and fast. This is going to a very brief overview. The internet is riddled with guides to composing photos - if you want more detail, just search youtube for 'composition in photography', watch one, in fact watch a few of them if you fancy it. The issue I have with it is you need to go out and take photos to see what works for you, a lot of youtube photographers end up being a bit dreary.
Regardless, a few things always taught to beginners is the rule of thirds. When I started out, I generally used this rule, and often still do as it does give a healthy composition to the photo.
The rule of thirds stated that the interesting aspects of the photos should be present on the lines with the focal points of the photo should be on the intersection between the crossing lines. You can see this with the main satellite island present in the middle of the bottom right corner. The junction of the sea and horizon and upper part of the top island line up along the top horizontal line.
Conversely, it can be argued that it is not a good photo, and does not follow the rule of thirds exactly, however this again is entirely subjective. It is dependent on you and who you are presenting to whether the images meet the quality expected.
While there are hundreds of other methods of composing images, my favourite follows the swirl of the golden ratio. Based on the Fibronacci sequence in which numbers being subsequently added to the previous number plotted on a graph results in this swirl. The Italian Renaissance statistician identified that this sequence is present throughout nature and is actually very aesthetic. This image almost follows it with the red light and first set of lit trees on the left going round to the direction of the milky way. Again when applied to photography it's not an exact science (otherwise it is).
Sometimes you can get a pleasing image that wasn't intended to follow any compositional rules. Conversely there are so many different techniques of composition, one that you perhaps have never heard of can be applied to the image.
I would follow the overarching advice of just have a think about what you are taking a photo of, and what story is it telling. If it lacks a story, or seems like an uninspiring shot of something then you should just try again. The aim is produce images that are thought or question provoking, emotive, and have a narrative.