My opinion is that if you haven't done yoga before, don't start at home alone - all the more so if you've had issues in the past with injuries. I think one needs a really good teacher to show you where the focuses need to be in each pose. See if you can find a good studio (I would recommend Iyengar or Anusara, both of which really emphasize proper alignment) and do a few classes so you get some familiarity with how to cue yourself when you're practicing at home.