Don't look at the corners or the center of the drawing. Leave those till o the end, in case you don't find him in the donut-shaped area where you should be looking.
Why does this trick work? It's simple statistics. Whitenoise writer Ottermann summarizes Blatt's findings:
Most Waldo drawings have a 'postcard' from Waldo in the upper left corner that takes up about 15 square inches. In the corresponding area on the opposite page, Waldo only appeared 4 times, which is slightly less than he would have been expected to appear there had he been placed randomly.
In the 2.5-inch band across the center of the page, in between the two Waldo rich bands, Waldo only appears 8 times, or 13% of the time.
Only twice was Waldo placed within 1.5 inches of a corner.