This is how your Layers palette should look right now.
Open the image of the model then use the Pen tool (P) to draw a path along the edge of the girl trying to keep as much detail as you can so you can make a clean extraction from the background.
Once you’ve closed the path, right-click on the path then select “Make Selection”. Copy and paste it into the other document. You can close this image of the model.
After pasting your model into your original document, position this new layer under the “Adjustments” group. Resize it slightly so that it covers a bigger area of the canvas. You can resize layers with the Free Transform tool (Ctrl+T or Edit > Free Transform).
Next, sharpen (Filter > Sharpen > Sharpen) the model to enhance the quality of the image (You can repeat this filter by pressing Ctrl/Cmd+F). You can also place this layer into a new group (Ctrl/Cmd+G) called “Model” to keep things organized.
Select the Burn tool (O) then set your brush size to a small round brush around 30 pixels with a hardness of 0%. Lower the exposure to 12% then set the range type to Shadows. Gently brush along the darker areas of the skin to darken the shadows and give it a slight HDR look. We're going to do this directly on the models face so be careful to not overdo it.
Follow the example below:
Burn the shadows on the hands, especially over the wrinkles following the direction of the shadows.
Also burn over the hairline and inside the eyes.
Switch to the Dodge tool (You can also hold shift while using the Burn tool) then change the range to "Highlights" and exposure to 9%. The brush size and hardness should be the same. We're going to do the same we did with the Burn tool except this time we'll be dodging over the brightest highlights in the image to give them more punch.
Here's the before and after comparison of this dodge/burn technique..
Now we're going to increase the vibrancy and brighten the eyes. To do this, select the Brush tool (B) then switch to "Quick Mask Mode". Brush over the eyes then turn Quick Mask Mode off by clicking on the quick mask button again. You'll get a selection of the eyes. Invert the selection (Ctrl/Cmd+Shift+I or Select > Invert).
Use the Hue/Saturation tool (Ctrl/Cmd+U or Image > Adjustments > Hue/Saturation) to change the color of the pupil to a vibrant blue.
Use the Brightness/Contrast tool (Image > Adjustments > Brightness/Contrast) to brighten the pupils.
Switch back to the Dodge tool and dodge the eyes to make them brighter.
Create a new layer on top of the model and clip mask them together.(Click between the layer thumbs while holding Alt):
Change this new layer's blending mode to "Overlay" we are going to paint some Shading and light to match the background on the model. Select the Brush tool with a brush of about 500 pixels wide and 0% hardness with the opacity set to 25% and change your foreground color to black.Now softly brush over the right side to shade it.Brush over as many times needed to get the result like shown below.Once you are done with this,Change your color to white and add some light to the right side of the model: