-Open novel to a random page
-Read a couple paragraphs, or at most, a couple pages
-Can you tell what the conflict is, or what the character is yearning for? Can you explain, in just a few words, what these paragraphs are doing and why?
It can be as concrete as "she is trying to catch the rattlesnake" or as abstract as "he is struggling to understand his son's anger".
I've encountered more or less this advice before, but it's a good reminder--and a hard pill to swallow.