I always put my windows about half open- enough to see my sight and allow the arrow to pass as well. Make sure you wear ALL black- including on your head. I never hunt out of a blind without all black on. Also- Sit towards the rear of the blind and not right by the window. That way there are more shadows on you and your uncovered parts (i.e. eyes)
...and on that day when my strength is failing, the end draws near and my times has come, still my soul will sing Your praise unending, ten thousand years and then forevermore!