Here are some of the secrets behind creating this style of art, using brushes and colour adjustment layers
These two elements are very important. Good tools to use are a graphics tablet and a mouse.
Start by adding a new layer and trace over the photo with a low-opacity brush. Duplicate the layer and draw all other details, such as hair and eyes, on top.
Next, duplicate the same layer again, use a mouse to draw the thicker strands of hair and then a tablet to create the finer ones.
Merge all layers using Cmd/Ctrl+Shift+Opt/Alt+E and reduce the opacity of the layer.
Apply the skin colour, shadows and hair tone by sampling as you go, using Opt/Alt and the Brush tool, then merge them.
The trick is to use the Color Balance, Hue/Saturation and Selective Color adjustments, with blend modes to create an artistic pattern.
Last, sharpen the image by going to Sharpen>Unsharp Mask to make the painting look authentic.