First of all we will create a document of width:480px and height:638px. You can create your own document, its completely upto you.

Open this potrait using photoshop, since it is quite a large image, we will resize it. Keep this image as the background layer.

Create a new layer above the background layer. Then go to Filter>Render>Clouds. Set the foreground color to black and background color to #ffecd1.

Set the blend mode to Saturation and opacity to 50%. Hit Ctrl+E to merge both layers. We will be having something like this...

Hit Cmd,Ctrl+J to duplicate this layer. Now press Shift+Ctrl+U to desaturate the image.

Duplicate this layer (Ctrl+J). Press Ctrl+I to Invert the layer. Set the blend mode to Color Dodge. Then go to Filter>Other>Minimum 2. Double click on this layer panel and set the blending option as shown. Alt+Left Click on the triangle to adjust the levels.

Merge both the layers (Layer1 and Layer1 copy) to bring out this effect.

Select this merged layer and Ctrl+J to duplicate it. Select this duplicate layer and then go to Filter>Blur>Gaussian Blur, select the radius to 6. Set the blend mode of this layer to Linear Burn. Then select the background layer and Ctrl+J to duplicate it. Bring it above all the layers and set the color mode to Color.

Now we will mask the background copy layer. Go to Layer>Layer Mask>Reveal All. Fill it with black color. Then click on the image on th left hand side of the background copy. Go to Image>Adjustment>Curve and set the curve as given below.

Now create a new layer and fill it with color #ffecd1. Change the blend mode of this layer to Linear Burn.

Select the background copy layer. Click on the mask. Now with the mask selected, take a brush of 45px softness and 60% opacity, brush the face portion of the portrait. When done select layer1 and change the opacity to 70%.

That's it!! We have our very own watercolor portrait ready.