My process is super simple. I stick to two to three layers and work my way up from the base, adding objects, light and shadow as I go. I use gradients, transparency, and blend modes to achieve the desired effect. I use the reference image on the artboard or an opposite screen. I never trace elements from my photos, but prefer to eyeball the general look to relay more emotion to the viewer. I also try to add a slight twist, such as the eyes in this one. I then used Photoshop to add noise and do a basic colour pass.