The selection may look perfect, but if you zoom in you can see that it may not be especially if you're trying to mask hair. To fix this, choose Select > Modify > Smooth and smooth the selection by 1 pixel. This will remove all tiny dots without making the selection too round. Making it too round will cause problems with the hair later.
Step 4 - Create a layer mask
First, to create a layer mask, you will have to unlock the Background layer. To do this, double click on the layer and a window will appear with the layer settings. Just click OK with the default settings.
Now choose Layer > Layer Mask > Hide Selection. This will create a new layer mask with the selected area (the background) in black.
Step 6 - Manually paint the mask to correct errors
Hold the Alt key and click on the layer mask thumbnail. You should now see the black and white layer mask in the document window. You can see that the mask is not exactly perfect. For example, the red lips was masked out because Photoshop thought it was part of the background when we used the Color Picker tool. To fix this, just paint it out with white using the brush tool. But make sure that you're working on the layer mask and not the layer.
