Review your image carefully — often there are simple adjustments you can make to make your overall image stronger. Lessen the saturation of a bright background object, blur unimportant details, and clone out distracting elements.
Portrait retouching has become a hot-button topic, but if you are using a high quality camera and lens, you often capture much more detail than you would ever notice were simply chatting with your subject over a cup of coffee. In my opinion, subtle retouching is as essential as good lighting and wearing make up for a shoot. I like to reduce the appearance of pores, soften any discoloration under the eyes and clone out any stray hairs from the face.
Your color choices do a lot to determine the mood of your portrait. Warm tones will imply happiness & health. Cooler tones will create a moodier, more complicated interpretation. Adjusting colors can also help to pull an image together, creating an overall consistency of tone. For most portraits, I recommend increasing the saturation slightly in skin tones to add more vibrancy. Be careful not to overdo the saturation or color toning, too much of either will create skin tones that are not realistic or appealing.
Adding subtle sharpness to the image, brightening eyes, dodging and burning, selectively adding or reducing saturation, fixing any color casts are important steps to ensure that your image looks truly professionally finished. Paying close attention to little details can really make a big difference.
While you should always think about your composition in camera when composing an image, experiment with cropping to make your composition even stronger. Make sure to straighten out the horizon line if you are shooting a full body shot and take care that you are not cropping off limbs at awkward spots (for example, cropping the bottom an image at the your subject’s ankle). Additionally, try adding vignettes to really lead the eye toward your subject.