Stock photography welcomes space and simplicity.
Designers like the shots to be simple because most likely they are going to do something with those photos – edit them, paste them into a design, adjust colors, add some text, etc. So it is a good idea to keep the scenes simple and clean, without too many details.
Another technique is to leave some space around the subject when composing a shot. This area is called “copy space” and can be used to include some text or other design elements. For example, if you shoot people outdoors, leave enough sky in the picture and some space around the people to make the shot “breath”.
Here are some examples of beautiful simplicity: