Firstly, always take 5-10 minutes to plan what you are going to write, on a spare piece of paper. Structure the essay to include: an introduction, a main body and a conclusion, and briefly write a note of what you intend to include in each section. This will make the essay flow better, which is one of the points that examiners look for.
The introduction should always briefly describe the key words in the question. It should also explain why the topic is important, and finish by describing what shall be discussed in the following paragraphs.
The main body should be split into a paragraph representing each key point chosen to answer the question. The main argument should always come first. A point should always be supported by an example or, preferably, a case study; giving multiple examples is a good way of showing additional reading. Including recent relevant geographical news (e.g. recent volcanic eruptions) is a great way of showing to an examiner a broad interest in geography.
The conclusion should summarise the key arguments and refer to them in terms of their importance. It is a good opportunity to highlight any ambiguity within the discussion, and consider any conflicting arguments.