I went to a powerlifting gym in Japan and worked with a guy who got a silver at the IPF Worlds BP Championships a while back. It was a great experience and I learned a lot.
One of the things he told me that instantly helped my arch and upper back tightness was to concentrate on pushing my shoulders downward towards the hips. They also used PVC to loosen the back as well:
A child does not learn to squat from the top down. In other words, he does not suddenly make a conscious decision one day to squat. Actually, he is squatting one day and make the conscious decision to stand. Squatting precedes standing in the developmental sequence. This is the way a child's brain learns to use the body as the child develops movement patterns. Therefore, a child is probably crawling, rocks back into a squatting position with the back completely relaxed and the hips completely flexed, and stands when he has enough hip strength. This approach makes a lot of sense and can be applied to relearning the deep squat movement if it is lost. -Gray Cook
Lifting Clips: http://www.youtube.com/profile?user=johnnymnemonic2