Do some research on "Walk Back Tuning". Basically you shoot several arrows at the same point of aim and see how they pattern; it will tell you what needs to change and by how much.
I recommend not getting too perfectionist with it. A couple years ago I was trying to make it perfect, and I ended up getting it way more screwwed up than when I started. Now I shoot a few times each week, and try to shoot several arrows at 10, 15, 20, 25, 30, and 35 yards. My arrows seldom hit more than a couple inches right or left from any distance, and they group tightly, so I don't try to get them any better than that. One distance may be a slightly different angle than another, but all the arrows in each group are parrallel, so it's consistant.