Some marks are lost long before the exam. Others are lost in the hall.

There is no universal number — it depends on your accuracy. The useful version of the question is: at what confidence should you attempt? With +4/−1 marking, a guess between two options is worth attempting; a guess between four is not, and the aspirants who lose most to negative marking are the ones who cannot tell those two situations apart in the moment.

It is usually the single largest recoverable loss on a scorecard — commonly ten to fifteen marks a paper. It is also the cheapest to fix, because it needs no new syllabus at all: it is a decision rule about when to attempt, practised until it holds under pressure.

Strongest subject first is the common advice and it is roughly right, because it banks marks while you are freshest and settles your nerves. What matters more is having a fixed order you have rehearsed in mocks, so the decision is not being made for the first time in the hall.

By treating them as a pattern rather than bad luck. Log them, classify them, and you will find they are a handful of repeating types — sign slips, misread conditions, unit errors — each with its own fix. "Be more careful" is not one; a reading protocol for the last line of a question is.