It's easy to get so caught up in photographing a subject that some uninteresting features or clutter within the frame go unnoticed. That is, until later, when you are looking back at your images and think to yourself "I wish that wasn't in the photo."
Whether you are composing through a viewfinder or an LCD screen, always be aware of any unnecessary clutter in your scene. This clutter could be unattractive things such as power lines, or other things that just detract from what you want the main focus to be, such as people.
Regardless of your composition, remember that simplicity makes for a far more powerful composition.
This image would have been better if the other items were removed from the table around the cake.
By only having the subject in the frame against a clean background this photo is more eye-catching.
1) Where possible try moving your subject to a simple uncluttered background.
2) If the subject is fixed, try a different angle or viewpoint for a simpler background.
3) When it is not possible to remove the clutter from the background, select a wider aperture to narrow the depth of field. This will blur objects behind the subject, and emphasise the foreground.
You may also be able to crop a photo or remove items in editing programs, but it's always better to try and get it right SOOC (straight out of camera) when possible.