If you're new to yoga I highly recommend setting yourself up with a good introductory or basics class at a local studio. For less than $20 you can dramatically affect your competency and learning curve with an instructor that knows how to teach the basics and helps you create a solid foundation for yoga.
Your BEST option of course would be to schedule a private lesson (or two or three) with a recommended instructor to REALLY get your feet wet properly as well as start understanding the prescriptive ability - in other words, create a practice that is personal and theraputic for you, just you.
A centrally located studio, Ginseng Yoga, offers monthly introduction to yoga classes on the first Saturday of each month (first class if free) from 12-1 pm. They also have a number of "beginner" classes during the week that can be a welcome refresher even if you've practiced yoga for a while: Monday at 4:30pm is Yoga Basics, Tuesday at 6pm is Fundamentals, and Saturday at 11:30am their signature style, Deep Yoga. Check it out: http://ginsengsandiego.com/newtoyoga.php.
Another studio this time in downtown Cortez Hill, The Little Yoga Studio, holds special Absolute Beginner's Workshops a few times year. For $25 you get a two-hour session with studio owner Maria Camacho that breaks it all down for you, making yoga that much more approachable, enjoyable and fulfilling. Upcoming workshops are scheduled for September 9, 2012, March 10, 2013 and April 21, 2013 from 1-3pm. http://www.thelittleyogastudiosd.com/events.html
Of course you can always join me at Fitzee Foods this September and October (schedule here) for free community yoga for everyone. I have an eclectic style in which I tend to break down each pose into it's different mechanical components to help you better understand what goes where and why, and I offer modifications for all levels, from beginner on up. They have classes 7-8pm every Monday and Wednesday, and I'll be guest teaching the following days: 9/5, 9/10, 9/17, 9/26, 10/1, 1/8, 10/15 and 10/22