Back hyperextending during handstands

I believe my back is arching too much from handstands as my back is slightly pained after a session. I read somewhere that to keep it flatter you have to look "forward" (if you were standing upright then someone turned you upside down but you were still looking the same direction). Is there any other tips/techniques to keep my back flatter? Also what are common causes of this over arching of the back? 

If you go to the handstand section or digital training section and look for feedback given on handstands you will find what you are looking for. But very shortly, your back should be completely flat with no arching at all! That will take away your lower back pain.