If you're a portrait photographer, you should know that there are a handful of incredibly common mistakes made in this field- and they're usually really easy ones to avoid. If you want to improve your compositional technique and produce the most flattering shots of your subjects and clients, bear the following things in mind:
First, it's important to be mindful of where you place your subject within the frame. When composing, a very common mistake made by amateurs is to leave way too much space in the frame above the subject's head. This is often empty, useless space with no added visual interest, and it's something you should be careful to eliminate. Emptiness above your subjects head is going to detract from your photo quality, so be mindful of that moving forward.
Beyond the space directly above your subject, it's important to consider the background as a whole. If you keep too much detail in focus behind your subject, the result is too busy. To eliminate distractions, use a longer lens and eliminate background elements with a gentle blur.
Finally, be more thoughtful with your shutter speed choices. People are difficult to photograph sometimes because of their inability to stay completely still- especially if you're working somewhere other than in a photography studio. To preempt this, use something more like 1/250th of a second to keep your composition looking crisp and clear.