Hi, I'm working on my anatomy, specifically facial anatomy. I've really only done landscapes so I've been having a hard time learning to draw the human form. I've been following several anatomy books, but its always nice to have other people take a look and give their critique.
I would do more proportion studies focusing on portrait like your doing. Trying to find basic shapes, focusing on length, size, and proportions. When you get the understanding of that move on to anatomy. Once you get the hang of that you can apply that onto your characters. Then getting into gesture studies and learning the foundations. Just keep on drawing and you'll get better. Welcome to CA.org, and Good luck too you.
I'm not sure from your post if you want to learn to draw a human face "from memory", or get better at portraits from life or from photos.
For the former, I recommend combining what you learn from Anatomy books with a lot of photo reference: don't just "copy" the face, but try to build it according to what you learn. Start with some guidelines to get the features in their right places, and always try to understand *why* things look the way they do, instead of just copying them. As for reading material - I haven't tried them, but I keep hearing Andrew Loomis' books are excellent.
For the latter (drawing realistically from life), here's an advice my art teacher in highschool gave me, which made my portraits much better: don't think of the face as a bunch of lines, but areas of light and shadow. Take a look at your face: the eyes aren't really outlined with a single stroke, and neither are the lips or the nose. They're all made of hills and valleys, defined by how the light falls on them and not by a "cartoon" pencil line.
That being said, I like your Indiana Jones and the 3rd portrait (she looks familiar but I can't place her...). Good luck!