I read thru the exam entirely (speed read thru some exams, but others like accounting I slow down coz it's the little things u miss that lose marks).
I work out the method I'll use 2 answer each Q, work out which 1s r easy and I'm confident with (I tackle these 1st come writing time), and re-read thru the hard 1s a couple of times 2 get my subconscious thinking bout how I can actually answer them.
Then I answer the MC that r theoretical (like, u don't have 2 do maths or something 2 work it out, jst read thru the options).
That usually uses up my reading time, but if I still have time left over then I might start 2 answer the MCs that require writing (mental writing... lol).
Like everything, it's personal preference.
Some ppl need 2 read the exam 2 calm the nerves - actually seeing Qs they can answer helps.
Others jst like 2 focus on 1 Q @ a time and start answering in their head from the start.