As lm said, big subject. My OH is a fitness instructor, but I wouldn't presume to pass on 2nd hand any of what I've gleaned from her - I'm crap at stretching, when I even bother doing it
However, I found this site a good help...
http://www.stretching.name/ - it's image based and you can build your own routine and save it, but hands-on tuition is always good for the basics.
Longer term, yoga and/or Pilates is the way to go imho. Pilates good for spinal rehab and core strengthening, yoga for overall flexibility and balance. Big investment, and tough to stick with at first, but you get a lot back.