Is this one of the most important of all? This isn't just photography however. The art masters, through the ages, have used the rule of thirds in their work - yet many photographers, amateur and professional alike, forget to use them.
This doesn't always suit an image. After all, learning to break the rules is also important. But it's a great place to begin.
What is the 'rule of thirds?' Essentially, if you divide up an image into a grid where the height and width are divided into 3, you have your start. iPhones actually have this grid built into the native camera app - it's often disabled in the settings however. To use the rule, simply place your horizon on one of the lines - approximately. (In this case the horizon is subjective - but I chose the waterline for balance). This technique alone makes a huge difference to many a landscape image.
To further make use of it, we use the parts of the image where the lines intersect. These are where we try to place the subject of our photograph. In the image below, I allowed the boat to make it's way to that point before taking the photograph.
Take a look if I crop it and move the horizon to the centre, how much weaker the image comes.
With a human, you'd often place the eyes of your subject here. This is an iPhone 'selfie' taken late one night with just a single light bulb for a light source. It just doesn't work if I place the eyes in the centre of the image. Because it was low light and therefore noisy, I converted it to B&W.
As always, if you find any of this remotely interesting, please upvote it and spread the word. It's very much appreciated.
Ciao - Andy