Now that we understand the pattern of the questions' format etc, it's easier to answer them. For anything else that I'm stuck at, I usually go to the unofficial clues sites such as student-rant.blogspot.com or any others listed on wikipedia under "da vinci code" entry.
I find the observation the hardest usually. It's hard to spot the right features at times and the clues help me enormously. Second hardest the geography. Third is chess (the guessing of questions that is, i'm no chess player...), but the questions ' answers can be found either through the movie site or wikipedia's da vinci code site.