It’s very easy to press the camera shutter button once we’re happy that an image is properly focussed and then forget to check whether the composition can be improved. Often this can be simply moving the subject out of the middle (the bullseye shot).
The thirds rule (well firstly it’s not a rule it’s a guideline) can be really helpful here – if you work in Live View with a DSLR or work off the screen with a mirrorless camera (e.g. a Bridge or CSC camera) you may even be able to select a thirds grid for the screen. I so often see images which have great content which have had little thought about composition. It can make the difference between a good shot and a great shot. Just remember to check and perhaps avoid placing stuff in the middle. Sometimes the bull eye shot works but it often doesn’t
Of course the best composition may also depend on other elements within your image, like the balance of the objects making up the image, any perceived movement within the image, or even if the shot is in colour or black and white. They will all have an impact on what composition will or won’t work. Here are a couple of useful links: