I'm sharing some composition tips to get better images, although I know most of the time you can't apply these tips for microstock photography, but they should help you to get better images.
1.- Rule of the Thirds:
Some say it is the most important rule of composition, here you have to imagine that your image is divided into nine equal segments (on the image draw two vertical lines and two horizontal lines). And try to position the most important element of the pic touching 2 intersection points. The most important element of the image should be on one side (right or left), never on the center of the image.
2.- Balance Elements:
Using the Rule of the Thirds can leave a void scene and make the image feel empty. So you should balance the image including another object of lesser importance to fill the "empty space".
Symmetry can be natural or man-made, they can be very eye catchy and make an image look full of details.
4.- Leading Lines:
Our eyes naturally "follow" lines. So you can use the lines on your photography to pull the attention to your image, lines can be straight, diagonal, curvy, zigzag. Use them to enhance your composition.
Many times when we shoot an image we found out that our image lacks impact because the subject blends into a busy background (of course you can always use PS to isolate the subject). So you have to look if you can, for a plain background.
Photography is a two dimensional medium(Now companies are working to improve 3 dimension photography), so you have to try to create on your images depth including images on the foreground, so you can have layers. Human eye recognizes these layers creating an image with more depth.
Sometimes a photo will lack its impact because the main subject is small compared to the rest of the image or its surroundings. By cropping tight around the subject you can eliminate the 'noise' (background), making sure the subject gets compete attention.
You can look for objects to frame your image, these objects can be trees, holes, etc., and what they do is isolate your main object and draw all the attention to it.
9.- Position of the eyes:
When making a portrait the eyes always have to be above the center line of the image.
Digital photography allow us to take plenty images, so always try different shots of the same subject and later on your computer analyze which looks better. Take advantage of your intuition and enjoy your photography.