Colour Picker To Define Colour Range - (Select one colour from skin, then and use the + selector to hold the mouse and drag a line over the skin to select the whole range of tones. Vary fuzziness to increase selection and smoothe. Click mask to create a mask with this selection)
Quick Mask - Use the smallest brush so that you never touch the background.
Content Aware Fill - and patch tool
Always add the background as soon as possible and do all your selecting and masking with it in place. This will prevent you making a mask which you think is OK, only to find out later that there is a colour fringe around the edge.This is especially important with hair, which is particularly prone to this.
If the edge of a mask is too sharp use the Blur Tool but unlink the Layer Mask from the image first. (Ref 12:00). Does this need doing whenever a Layer Mask is edited? ***
You can edit this mask by painting on it with the Brush Tool using wither black or white.
You can select specific areas on the Layer Mask to Paint on using the normal Selection Tools.
You can use a new selection to limit where you can paint, and in this way add or subtract selected areas of the mask to refine a selection e.g. by selecting better hair detail to add where a person's body is already cut out well.
Similarly you can still paint on a Layer Mask when its icon is selected but its image is not in the main window. Here you will see the changes made to the mask reflected in your image.
Look at the Properties Panel to feather the mask and adjust its density. Can also open Select and Mask from there, Colour Range and Invert.
Using Apply Image to Create a Mask
Apply Image can be used to stamp any layer onto a new layer. or onto a mask This can be very useful for creating very selective masks which use actual image pixels to create the mask, and so are very accurate.