Past papers. They are the key to being good at maths, for the most part. Practice full papers - if you run out of time, continue in a different colour pen so you can see how much you know versus how much you did in the time. That way you can better manage your time.
Focus on the areas you know the least! There will be plenty of resources, whether that be stuff from your teacher, textbook, or online, that provide plenty of topic-specific questions. Do them over and over and over until you know them back to front.
If you really struggle with long, worded questions then start each question by identifying what area of maths you're looking at. This can make the question less daunting. Break down the process into steps, and lay them out clearly (e.g. for solving a quadratic, it could be 1. identify a, b and c 2. plug them into the equation 3. solve for x). If you always have the same process you follow, it'll be easier as you won't have to panic in the exam.
If you're in a rush and don't have time to revise everything, revise algebraic manipulation (solving quadratics etc), and trigonometry. These are big topics on the paper and by getting these down you'll get lots of marks.
Make sure you read the question correctly! don't forget a negative, or move a decimal place! highlight important parts of the question if this helps.
Learn your circle theorems! Memorise what you're looking out for, and what they mean (e.g. cyclic quadrilateral means that opposite angles total 180 degrees). Practise these lots, as the only good way you'll get good at spotting them is if you practise.
Best of luck (: