If the contrast between hair and background is strong, cutting hair is easy. Just use Quick selection tool and Select and Mask like this page.
But the typical image is more vague.
How about this image?
This old woman’s right side hair is difficult to see. If you try cut her hair by Quick Selection tool, you will get a image like below.
the right side hair is apparently bad. So want should you do?
One way is using other parts of hair instead. Use the left side of her hair for the right side.
I explain step by step.
At first, create the selection her hair by clicking the layer mask with ‘Ctrl’ .
Go to ‘Select‘ and choose ‘Transform Selection‘
Now you got the selection of her hair. And you can transform this selection freely. For example, choose ‘Flip Horizontal‘.
You could move the selection. And Choose white brush, and Pint inside the selection.If you mimic this process several times, you will get better image like below.