Starting with the sketch. I didn´t captured screens form the background panting process, sorry. And sorry again for the refference, I don´t remember who the owner is. But it´s only for autopromo non comercial proposes.
The skin, first only with general colors. Placing light and shadows.
Detailing the face. The most important thing on this piece. Specially the eyes.
Painting the hair.
A few details, here the apple. Making the shadows with the opposite colors, in this case blue / cold tones.
Detailing the hair. Is a slooow process.
And that´s it. Painted fully in Photoshop CS6 and a Wacom cintiq.