There are a number of ways you can do it, depending on the level of realism you are trying to achieve. The best way is probably to solve the problem during the initial photoshoot. Take a picture of your human model's face from straight in front, from 45 degrees to one side, and directly from the same side (90 degrees). Then you build an entire half of the face by putting pieces from those three pictures onto three separate layers and blending/erasing/cloning.
If getting pictures of the face from three different angles isn't an option, then obviously the above example won't work for you. If that is the case, I recommend using the lasso tool to copy a decent sized piece of the face to a new layer. Don't copy from the area just under the eye or right next to the nose, because those areas tend to have more texture (obvious pores) than the rest of the face. Try to copy from an area closer to the cheek or chin, if you can. Once that area is copied to a new layer, duplicate that new area and move the duplicate image slightly away from the original copy, causing the original copy to look larger. Make sure those two layers overlap and then blend them with erase and/or clone. You may also have to use the dodge/burn tool to lighten/darken some parts because it is amazing how much light differential there is on a human face within just one inch on a photograph. Once you've blended those two layers, merge the top one down to the original copy, but don't merge the original copy down to the main portion of the face yet. Instead, now make a duplicate of the new merged section. Move that new duplicate slightly, then blend again, then merge down again, continuing this process until you have a fairly large piece of manufactured skin to stick pretty much anyplace you want (including the top of the neck section, once you get to working on the body).