What is the level of your knowledge about that subject? It also includes Practice, Test, Revision, Recall, Notes, Whole your knowledge or study management system.
Solve Puzzle tests. It will improve your question understanding up to the surprising level.
Learn memory improvement tricks that will improve your information absorption skills. Read in detail here: "How can you learn faster?"
I am explaining further with my subject Quantitative Aptitude.
If one wants to understand quantitative aptitude questions easily then here are some suggestions that can help.
Solve different types of questions.
classifications of questions. You should be able to find the type of question at one glance.
Systematic expand your knowledge. First, solve One Liner Questions. Then level I, Level II, Level III and so on..... If you will not follow this then you can face problem understanding Question of Level III if you skipped Level I or II.
Basics and Concepts clarity, understand formulae, understand each step of the solution.
And again data retention also depends on practice. I am giving 2-3 simple examples.
In a small restaurant, waiter remembers all foods material served to many persons at the same time. And all thing he does mentally.
One student of 4th class was unable to understand even simple questions of additions, subtractions but he was able to calculate the price of sweets purchased by a customer. [ for a normal person it becomes very difficult to find the quantity for Rs. 51 if Price is Rs. 170 per kg. Or What should be the charge for 615 gm? And surprisingly he was able to do very efficiently very quickly and mentally.
So apply your knowledge in real life or connect with real life. Develop your common sense, develop the presence of mind.