One of the last components of great portrait photography is style. Style can really shape the affect a portrait has on a viewer. Often a portrait can be connected to the photographer simply because of the style.
Style is the photographer’s own interpretation and use of lighting, exposure, posing, image editing, and other aspects of photography. Style can be unique, copied from another photographer, or adapted from a number of styles.
Style often is influenced by personality. I am more conservative and low key. My style of photography tends to be more traditional in nature. Your style may be vastly different from mine. Perhaps your style will evolve over the years from personal photography experience, and from the influence of other photographers.
When starting out as a portrait photographer, I think it is important study portrait images you admire. Evaluate the reasons you like that particular style. I don’t have a problem with trying to mimic that style either. There is an old saying “Imitation is the sincerest form of flattery.” When you are first learning lighting, posing, and image editing, it is helpful to study and copy others. As you grow and learn, you will find that you eventually start to form your own personal style.
Some photographers can produce multiple styles in their work. There is nothing wrong with this either. If you desire to become a professional portrait and/or wedding photographer, you will have to decide if you will market a certain style, or if you will offer a broader range of styles.
As far as things to worry about, I believe style is the least important. Many people waste so much time trying to develop a unique style. Concentrate on learning and perfecting lighting, exposure and posing, be yourself, and your own unique style will soon follow.
Most important to remember—Have fun!