There is no perfect, one-size-fits-all strategy. You need to figure out what works best for you. Here is what I've found useful:
Read the first question.
Start reading the case and identify the relevant data for question 1.
Answer question 1.
Read question 2.
Continue reading the case till you find the data for question 2.
Answer question 2.
And so on...
Generally this strategy works because questions are aligned with the order in which information is presented in the case.