Most people attack a hidden object scene by letting their eyes roam the whole page. It works for the easy finds, but the last few objects always seem to vanish. The fix is to stop searching the whole scene and start searching a quarter of it.
Divide the scene into four
Imagine a cross through the middle of the page, splitting it into four quadrants. Pick the top left and give it your full attention. Ignore the rest of the scene until you have finished with that corner.
Scan each quadrant in rows
Inside a quadrant, move your eyes left to right in narrow bands, the way you would read a paragraph. This stops you skipping over the same busy patch again and again.
Check the object list against the quadrant
After each quadrant, run down the list and ask: could any of these be hiding here? Objects are often disguised as part of something else, so look at shapes, not just colours.
Look at edges and outlines
Illustrators love to hide items along borders, inside patterns and in shadows. Pay special attention to curtains, rugs, wallpaper and crowds, where outlines blend together.
Rest your eyes between rounds
If you get stuck, look away for a minute and come back to a different quadrant. Fresh eyes spot what tired eyes miss.
Put the method to work with Lost And Found, full of scenes built to reward careful searching.