First you’ll need a good photo reference. For this tutorial, I decided to create a self portrait, so I requested a little help from a friend of mine to get the shots.
Important tips here are to use perspective to show depth, have a good variance of light and shadow, and try to ensure your model has some hard-edged accessories that will contrast with the softness of skin and clothing (such like glasses, jewellery or a starched collar).
From these photos you’ll need to choose the best fragments to combine in a single image that will form your main reference. As you can see from this screenshot, I’ve chosen the face from one, glasses from other, and other details from other shots. Be picky in this stage, it’s well worth it.
For each part, roughly crop around the part your want. Then open a new document on Photoshop with a black background, and place each of the elements on separate layers.