Get the wind and your approach right, find the right tree and it'll be just a matter of time. Scrape hunting can be very frustrating. Don't hunt individual scrapes, because they probably don't mean much. Look for scrape lines in many of the same places you look for rub lines. Scrape lines along ridges, the edges of clearcuts, old logging roads and fencelines can be good spots.
Bucks often abandon scrapes altogether when does start coming into estrus.
Right before the rut starts to get into full swing, bucks will work scrape lines most heavily. More than one buck will work a scrape, so be patient if you're looking for a particular buck. And a trophy buck is just as prone to make a small rub as a large one. The size of a scrape means even less. Most of the really big scrapes that I've found were made at night with no pattern in their placement.