Just try it
One of the most common ways for candidates to lose marks in exams is because they say things like, “I can’t do it”, “I don’t understand”, or, “I haven’t done a question like this before”, before they’ve even tried. This is very common in multi-mark Maths questions, but even in English questions too.

Maths questions disguise the curriculum
Good maths questions attempt to disguise the sort of question it is. It’s not always easy to look at a question and go, “this is a reverse percentage problem”, or, “this is a circle theorems question” like it is on a worksheet, where all the questions are teaching you the same thing. Sometimes it might be a mixture of topics, or it might be a topic in disguise, for example it looks like a geometry question, but it’s actually testing your fractions skills.

Hannah and her sweets
https://www.theguardian.com/science/alexs-adventures-in-numberland/2015/jun/05/how-to-solve-the-maths-gcse-question-about-hannahs-sweets-that-went-viral
This infamous Maths problem drove GCSE candidates to distraction. Eight lines of facts about a bag of sweets, followed by the command to prove an algebraic equation. Many candidates understandably gave up at this apparent non sequitur, and lost out on a lot of marks.

Play around
The candidates who scored high here were the ones who went, “Well this doesn’t seem to follow on at all. Let’s just play around with the information and work out what we know.” By just playing around (e.g. But exactly how many red sweets are there? Exactly how many are in the bag?), candidates would start to notice that the “n” of the algebraic formula and the “n” for number of sweets in the bag are one and the same. There’s no obvious way of answering this question until you start just moving numbers and letters around and see what happens. What’s the worst that can happen?

Just have a go in English Comprehension
The same applies in comprehension. Sometimes a passage might make no sense; packed with archaic or confusing language; impossible to understand, let alone explain to an examiner. Candidates who give up at this point are likely to gain no marks at all. Instead, why not have a go? Check the prefixes and suffixes: maybe you understand some of the word, if not all of it. What about the context; is it possible those unrecognisable words “loch” and “glen” are something to do with the countryside? Is the author trying to help the reader admire the countryside?

What’s the worst that can happen?
There are certain exams where candidates lose marks for incorrect answers (e.g. the American SATs) but in the U.K. these are few and far between. The only “wrong” answer is a blank space. Besides, in a five mark question, you only get one mark for the right answer; the other four marks are for your working. Even if you think you’re “wasting time”, your working could actually end up scoring you more marks than if you just put down the correct answer.

Encourage mistakes
One of the best things teachers and parents can do is encourage mistakes. Teachers often model “trial and improvement” questions by demonstrably getting the answer wrong several times. But if you don’t have a go (e.g. “I’ve no idea… maybe it’s three… let’s try and see what happens”), then you’ll never know. Praise your child for their mistakes, even if they don’t end up figuring out the right answer, and point out your own stabs-in-the-dark and estimation failures as often as you can.

The winning attitude
Top candidates don’t necessarily have more skill than average-level candidates, it’s more to do with this “have a go” state of mind. Do the easy questions first, and when it comes to the hard questions, just try a few things. One of them might end up being the stepping stone to a whole new world of understanding.