Intensifying the Story Problem
Question: During which time in the plot should you add elements to intensify the problem?Answer:
Generally speaking, the problem or problems faced by the characters should grow in intensity starting from the first page and continuing until they reach their most intense state at the climax.
That's not to say the characters won't experience small victories along the way. Sometimes they need rewards to keep them motivated, and sometimes readers need a little emotional change as well.
Think of the plot like a roller coaster or stock market chart which has many peaks and valleys but with an overall upward trajectory. You want to space the elements that intensify the problem throughout the story so the reader doesn't have a chance to get bored.
Also bear in mind that each event that occurs will change things somewhat. As a result of one thing that happens, characters will decide on a new course of action, which in turn will lead to a response from someone else. Attempting to solve one problem may cause new problems to arise. The idea is to keep the reader's interest and curiosity rising until the ultimate event that brings victory or defeat, satisfaction or failure.