I’m a firm believer in starting with an easy question: find a topic area in which you’re strong (preferably one with a short question) and answer that one first. It will give you a chance to earn some easy marks and, perhaps more important, to settle down. After that, I would work from my strongest areas to my weakest, but I know that some candidates prefer to work front to back; do whichever makes you more comfortable.
I’m also a firm believer in minding the clock. If you’re working on a 24-minute question, then once you’ve spent 24 minutes on it you should move on to another question, whether you’ve finished it or not. Time management is crucial.