I am speaking out of my photography experience so you can decide whether it's correct or not by yourself. Everyone do things differently.
1. Check for focus in the eye
If the focus in the eyes is not shape, the photograph probably out of focus.
So each time you are taking a portrait, always focus on the area near the eyes and nose area.
2. Reduce camera shake to get sharper image
As a general guide, always use a shutter that is same as or higher than the range that you are using.
For example, if you are taking a photo at 50mm, your shutter speed should be 1/50 or faster.
Well, some hands are more steady than others, so this is a general guide.
3. setting ISO, F-stop and shutter speed
My practice is to set lowest ISO against a set of f-stop and shutter speed possible.
For example, i will set a f-stop and shutter speed depending on the type of photograph I want to create. I will then adjust the ISO from a low number to a higher to compensate for the brightness required. But I will always use the lowest ISO possible.
4. Sharpness vs grain
As a general guide, always use the lowest ISO possible.
But if the shutter speed is causing the photo to be under expose, it's better set higher ISO than to try to steady your hand and lower the shutter speed. It's better to get a grainier photograph than a blur photograph.
5. use natural light
The subjects with their back against the light will cause them to be under expose. Unless you are creating a silhouette, the subject should always face the light. Put the light 45 degree to the subject to create shadows.
If the subject's back have to be against the light, use a flash to expose the subject.
6. use rules of third and fibonacci
Put the subject on the side is sometimes more attractive to the viewer than up front in the center.
Leading lines from the corners of the photographs is a good starting point.
You can Google fibonacci under image for example. They are example of leading line to the main subject.
7. Use simple background
A simple background allow viewers to focus solely on the subject. If there is a lot of objects in the back, viewers will tend to look to what is behind the subject.
If avoiding the object is impossible, you can try low the f-stop number and create a bokeh effect on the subject so to blur the objects in the back, making it not so obvious to the viewers.
8. Always bring extra
Always bring extra batteries, and memory cards along. Imagine waking up early in the morning all prepared to take a beautiful sunrise when your memory card corrupted or your battery ran out.
Bringing extras will save you a lot of disappointment.
9.Be trigger happy
Although this is not a practice of good photographer, it's good to avoid disappointment. Especially for event photography or sport photography.
With digital camera and cheaper memory card prices, you can take photograph more economically. It's better to get more photograph and choose the good ones later than to take one at a time and miss some shot which could be the winning photograph. Better your skill at getting higher hit rate though.
10. Enjoy what you are doing
Finally, it's really about enjoying photography. Don't feel like you are forced to do it. Remember why you pick up photography in the first place.
If you are tired, rest. Taking a photograph in lousy mood could affect the way you portrait things. You get agitated with your subject easily.
Art takes patience.
I hope you guess find these tips useful. Feel free to share more tips