I've always been one of those unlucky people who can't touch my toes.

I can't stand up, bend down, and touch them... nor can I sit on the ground with my legs outstretched and bend to touch them that way either.
I do exercise (both with weights and aerobic), but I don't stretch. Trouble is, I'm not sure exactly how to stretch, or what I could do to become more flexible in general. Any help?