I think this question has come up before in previous exam years (little fish, my eldest, took the 11+ Sept 2013).
Like others I'm a firm believer in quickly reading the passage through completely first and then working my way through questions - but have two wrinkles to this system.
It is worth checking the structure of questions - often in comprehension the first 2/3rds of questions are on the story and the last 1/3 is vocabulary related. If vocabulary is a strength or your fairly confident you know the meanings of the words listed - it may be strategic to go for vocabulary questions first and then comprehension questions. [In exam conditions the timing will be very tight so better to focus on the questions you can easily gain points from & then go back to more time consuming/ difficult questions]
In general comprehension questions tend to reflect the sequence in the text - so first questions are at the start of the text and last questions are at the end of the text. Use that structure to help you know generally where to start looking for your answer.
As ever with comprehension the answer is actaully in the text your job is to find text to support your answer.
Hope that helps
Thank you, great advice.