Thanks for all the detailed replies. Am I missing something? I mean structuring questions correctly to obtain full marks, consistent revision etc. But is there any real barrier to not getting a perfect if not near perfect mark? I mean surely this can be done by doing as many practice exams available and reviewing them?
imo, the potential barriers are mostly psychological ; If you doubt yourself, stress too much or just be lazy.. then you're probs not gonna get a 50. If you mean in terms of the subject, most sub's, esp eco, require specific language conventions ot be demonstrated to get full marks; you MUST word your answers in a specific way; check with past students who scored well or your teacher. Also, things like coherency, specificity, logicality and analysis are extremely important in getting that 50! <-- doesn't really apply to maths/sciences
tl,dr Give in as many questions as possible for your teacher to mark!