I wish I’d known as much about the way examiners think when I was doing my school exams as I do now. It’s actually ridiculously easy and it’s not so much about how much you know as how much you understand what you know. Here’s the white board just to explain what I mean.
This method is pretty much the same across all subjects, but especially the sciences. Normally, in real life you will do things the opposite way around: what is happening (the phenomenon), when it happens, how it happens and then finally why it happens. The aim of all investigations is to figure out the last thing, and it’s also the hardest to be certain about.
Anyhow, when you are confronted with a question, just remember the examiner usually wants to know if you know why something you have been asked about is happening (big marks), how it happens (more big marks), and then when it occurs, or occurred.
Sometimes the question might be “what happens when?” but these questions usually carry the least marks. I say “usually” because it does depend on the context. Anyhow, go into your exams thinking “why, how, when, what” over and over and then your answers will usually be good and solid. But do pay careful attention to the question. If the question is (for example, in geography) “what is the difference between the way a u-shaped valley and v-shaped valley is formed?” then you don’t need to explain the formation of glaciers, but you can just explain how a glacier moves and cuts the u-shaped valley, and then how a river does the same with the v-shaped valley, without describing in detail how rivers are formed, although you can allude to this.
Don’t forget, a picture paints a thousand words.
And most of all, use common sense. Scientific reasoning began life as common sense.