There are so many ways to make a selection in Photoshop that one might  need to make several tutorials, i`m not going to do that. In a sense we can use different techniques for different situations: for a quick selection my favorite is the quick selection tool and than i add or subtract from it with the lasso tool. For the most exact selection i use the pen tool to create a path and than transform it to a selection.

For delicate selections i tend to use the channels, especially for hair, and that is our example today.

We will start with the image we want to make the selection on.

The first thing to do is go to the channels panel and find the channel that has the most contrast in. The contrast level will depend on the image, so just cycle through the channels and find the best for your picture.

After you found the most contrasted channel duplicate the channel (ctrl+I) to create a mask. If needed paint with black and white to make the mask more accurate.

Now press ctrl + and click on the mask to make it a selection. And then select->reverse selection so that the black will be selected.

Get all the channels back to visibility and go to the layers panel. While the image is selected press crtl+I and there the model is separated from the background and her hair stayed nice.

In the case when there is an halo around the image go over with the burn tool on the edges. And viola we have a perfect selection.