I once read that Jack Sock strings all poly at 38 lbs and Daniel Nestor strings gut mains at 40 lbs with a poly cross at 38 lbs. Volandri, the Italian pro, has been known to string all poly in the 25-30 lb range. I don't think there is a right way. James Blake, Del Potro, and early Roddick use to string in the high 50s to low 60s. Roddick did drop about 10 lbs late in his career.
For me, I string poly between 46-52 lbs on 100" racket with 16x19 pattern. I think a reasonable range for 90% of us is 40-58 lbs. But, I would only go into the 54-58 range on an OS open pattern. I personally have not gone above 52 lbs on poly in the last 2 or 3 years.