Regular in submitting work.
Practise as much as you can under time pressure.
Read various sources of information on different topics to get a full grasp of the chapter you are working on and practise exam questions so you can see the range of questions that you can get.
Know your chapters and subject well and then attempt different types of questions under time limit. It is important to identify your weaknesses and work on them. Make sure you can attempt questions under exam pressure and within the time given.
There is no easy way for this. You have to be aware of anything that is going on around the world and improve your general knowledge. The topics you will get in exams may surprise you and to go around that you need to have good knowledge and ample facts to support your arguments. Try to remember a few quotes as well to add weight to your essay. As for comprehension, that requires practise and understanding.
Read! Read a lot. Improve your knowledge on the topics you are supposed to attempt. Make sure you have enough evidence to support what you are saying and the way to remember all of that is to write as many essays as you can. The more you write, the more you will remember.
Here is an inspiring Story that this Laureate is sharing with you...
Starting college, I wasn’t the brightest student. However, as I started doing the subjects I liked (Economics side), I found that I was good at these subjects and since then I decided that I would do my best. Do not be surprised if you find it hard. Most of us laureates are like that. We have struggled a lot to reach that stage but at the end, we are all proud of what we have achieved. I have shed so many tears over the course of these two years. I have felt discouraged many a times when I was too tired to even solve a simple maths equation. But what matters ultimately is you not giving up and being consistent in what you do. Whatever happens, DON’T GIVE UP!