For this I suggest that you open up a image of the HOP you are about to do next. There you can see all of the objects spotted for you already. Then it's just a matter of clicking on each.
You can also earn the achievement Without fail if you manage to complete the HOP with less than 3 mistakes.
Here is a good guide:
http://www.bigfishgames.com/blog/walkthrough/nightmares-from...