I get freezer wrap at any store like Wal Mart, or grocery stores. I have a square wooden rack I built that allows the paper to be pulled down thru and out the bottom. A couple shots, and I pull more paper thru and the roll feeds out. My rack is functional, but I rely on it so much, I should make a new one.
Blaino is correct about broadhead weight.
A decision needs to be made about what weight broadhead you will be using. I have used big two edge broadheads for decades. A big Magnus-1 or Zwickey Delta with an aluminum point adapter ends up weighing 175 grains...plus or minus a bit. So, I always buy 175 grain practice points.
However, sometimes the same arrow can shoot various weight points and not be affected.
Also, invest in practice heads of various weights...I did this, and trying different weight heads when tuning can answer questions quickly.
A good tear thru paper means the arrow is flying straight when it passes thru. A good tear produces a hole with damage done to the paper in the basic shape of the feather configuration. Enlongated tears will show up and you can make adjustments accordingly.
I get a good tear thru paper, and then screw on some big, wide, two edge heads. Take it outside, and back up to thirty, or thirty five yards. If your arrow is tuned, the arrow will guide the broadhead. If not, the big wing (broadhead) will do the guiding and you will see the arrow veer in flight. I have found that tuning problems show up when shooting longer ranges. Close range shooting can hide problems with broadhead flight. Big , two edge heads will show you tuning problems.
This method has saved me lots of time and headaches...PLUS, at any time, a bareshaft can be used to confirm what you find with shooting thru paper.
Shooting thru paper has taught me just exactly how important brace height is. I have a Predator also, and I have two sons who both hunt with Predators. I have found Predators to be sensitive to proper brace height. A brace height too low, can ruin a well tuned shot...just a thought.
I know this much...my broadheads and field points fly exactly the same. A broadhead that tracks to the same impact point as a field tip is a beautiful thing.
Sorry for the long post.