Hi to all! Here is your amateur adviser again:)
Composition of image is one of the elements that defines images aesthetic value. If you are shooting objects with purpose to be used by designers then some composition rules will not apply. You just center that thing on center, isolate it well and that's it. Designers will decide what to do with them during creation process.
Making impact to viewer is closely related to human mentality, sense of aesthetics, habits in observing the world around etc. Foundations of this knowledge was known even from old Greeks and was extensively used in art. Photography is one of the arts so visual impression principles applies to it as well.
I dont like the term "rules", but rather I use the term "principles". Understanding some basic principles gives you opportunity to experiment with them as they may serve you in both directions.
In terms of rules we consider them as "following" or "breaking" the rules. Both can make proper impact if you do this well.
Lets see an example: The "horizon" principle requires that your horizon on photo must be horizontal, at zero degrees. If your horizon is at 3 degrees angle it will look like a mistake. But you might express some action or movement by changing the angle of horizon which will emphasize and unbalance the image to give certain emotion. In first case, a boat on the sea will look good at zero degree horizon, but a man falling from bicycle may look more interesting with angled horizon, as our idea is to express unbalance. The principle here is that if you break the "perfect horizon rule", then really break it. Use strong angle so your intention is obvious.
Horizon rule is just one of compositional elements. There are many of them and I want to try to explain a few that are most important.
Rule of Thirds is one of the most famous compositional "rules" around. It says that center is not so valuable as are the sweet lines and sweet spots. Divide your image in three thirds horizontally and vertically. You will have like 3x3 net over your image. The lines between thirds are sweet lines, both horizontally and vertically, the points where lines intersects are the sweet spots. There are four of them and they are considered as most valuable positions on image. That's what the "rule" says, and in most cases it works. Which line or spot you will use to align your point of interest on depends on your object and scene. Note that symmetrical images, and mirror reflections likes center more then sweet spots, because centering emphasize the symmetry. Choice of spot really depends on the object and the impression we want to send out.
How are your objects positioned inside your frame? What are they doing? What is the main point of interest in image and how it interacts with background and other subjects? Is it interesting to look at, is it pleasant, does it bring any emotion? That is composition.
Regarding balance you must consider all graphical elements, namely lines, curves, shapes, verticals, diagonals, patterns, textures etc. Let your objects be aligned to them.
If you have faces on image, note that observer will probably follow the direction where your portrait looks. Many possibilities how you can get compositional advantage of this.
Move closer to the subject, fill the frame, avoid unnecessary intersections, and tree branches growing from peoples heads. Check the background, it is important what is seen behind your subject, Avoid busy backgrounds and unnecessary distractions which has nothing to do with your image theme.
One very important thing: if you need to "cut" human body with image frame, target for "bones", don't cut hand on wrist or elbow, don't cut leg on knee or heap. People will look like invalids. Try to play with cropping on your images and see the difference.
Take care of depth of field. Sometimes it is good and sometimes is pain. Depth of field affects environment of your point of interest, thus affects your composition
Choose interesting angles of your shoot. Image is more interesting if you record it from angle which is not common. Many have seen puppy dog from above. It is more interesting to lower your camera on puppy's height. You will make better impression on how the world looks like from that perspective.
Not all of this theories and ideas will apply for DT acceptance. There is a difference between RF stock photo and artistic impresion which you would like to sell for $500 for a framed wall poster. But lets put it this way, formula 1 pilot first must to know how to drive a regular car too. That is why we read, learn, observe, and then try to put it into practice. Someone succeed, someone don't. Otherwise, no one would buy, and everyone would sell.
Until next time - keep shooting.