When I first started getting into photography, I took an excellent online course taught by Scott Stulberg through Bryan Peterson School of Photography. It's a 4-week course, where you download a lesson (and he provides massive photo-filled PDFs with ideas and tips), an assignment and then get feedback from him (and get to see his critiques of other students). You get about 9 days to complete each assignment and he's very responsive and constructive.
Eye to Eye: Capturing the Face - face photography classes
Bobbi Lane teaches a 4-week course focused on posing and directing through the same school:
Posing and Directing Photography Online Course
I haven't taken this specific course, but I have taken a live course with Bobbi and she's an excellent teacher. She also teaches a portraiture course online (called portraits unplugged - using natural light). If you find that you learn best when you get a lesson and then an assignment to practice, these courses are great options. If you prefer to just watch a tutorial, Bobbi also offers an online videos for sale and has some shorter clips for free on Youtube.
With portraiture, I found that it worked best for me to learn about the following topics in this sequence. I think that if you pay too much attention to the light at first (especially if you're focused on flash and strobe), you'll miss out on the more fundamental elements of connecting with people and learning how to produce an attractive image
- Establishing a rapport with your subject (Scott)
- Composition, paying attention to which angles and lenses produce the most flattering images (Scott)
- Shooting in natural light, and natural light with modifiers like reflectors (Scott)
- Using flash and/or strobes (mainly Bobbi, although Scott also covers this in his last lesson)
- Environmental portraits (a live course I took with Neal Slavin)
- Posing and directing (Bobbi)
- More advanced lighting techniques (various sources)