There are some standard compositional rules that you should know well, as they will let you produce interesting photos most of the time. But they're not ironclad - when you know them well, you will begin to get a feel for when to break a rule or two to make your photo more impactful.
Rule of Thirds
Mentally divide your frame into 9 equal parts with 3 equally-spaced horizontal and 3 equally-spaced vertical lines. Place interesting subjects at the intersection of these lines, or along the lines themselves.
Fill the frame
Get up close to your subject and fill the frame with him, her or it. This technique reduces distracting background visuals and focuses your viewer's attention on the subject. It can be used in a variety of photographic styles and should be a mantra of every portrait photographer.
Don't cut off limbs
Cutting off limbs at awkward places can be very distracting.
L-R: Cut-off limbs vs no cut-off limbs
Give your subject space
If your subject is looking somewhere, give your subject space in the frame to look in that direction. It gives the viewer a sense of what the subject is looking at.
L-R: No space in the frame vs space in the frame
Use frames to draw the attention of the viewer to the subjects within the frame. Frames can come in all shapes and sizes, from artificial structures like arches to natural ones like foliage, repeating structures like street lamps, to body parts like hands or arms. In this photo, the neon lights frame the subject's body, and his arms frame his face.
Note: The subject of this photo is Adam Stamenkovic - he's an excellent photographer and a great friend. Check him out on Instagram.
Converging lines in your photo lead the viewer's eyes towards the point of convergence. Use leading lines to guide your viewers' eyes to the subject of your photo.
Have a clear subject
You can do this a few ways, such as by utilizing a clean background that isn't distracting. But if your shot seems messy, try isolating your subject by shooting it with your lens set to a large aperture and narrow DOF. This will blur out the background, filling it with smooth and creamy bokeh. Make sure your subject is in focus when you do this, otherwise all you'll be left with is a blurry photo.
Photos that are too busy and lack a clear subject generally aren’t engaging. So it's important not to confuse viewers. Be clear what you want to draw the viewer's attention to.
Here's a comparison of a messy photo without a clear subject vs a photo with a clear subject, using shallow DOF to isolate the flowers in the foreground.
L-R: Messy shot with no clear subject vs clear subject
Breaking the rules
Like I said at the start, these compositional rules are not ironclad. They are useful tools in that they help most of the time, and in most situations. So if you're not sure how to compose a shot, you can always fall back on them for a "safe" shot.
But photography is also an art, and sometimes, the rules just need to be broken to make your photo stronger.
Break them if you need to.
Please consider sharing your photos with the community by tagging #dharmaportraits on your Instagram photos - I'd love to see how you're using these tips to create beautiful photos.