My suggestion would be to pause for 3-4 seconds before each question for composure.
You can think of it as a waste of time but that helped me to reduce the number of mistakes I made in the quant (as I often would overlook some information or read the question wrong)
You also should memorize a few questions (both the question and the solution) so that you can reproduce it (e.g. groups questions, and so on). This will allow you to fit the question you are working on into a template - you can write out the equation or the formula for the question you memorized and then just plug in the numbers into this one. I did for the Group1, Group2, Both, Neither questions. Helped to keep things straight when I was under the clock pressure.
P.S. Also make sure you ALWAYS have the clock on. Book, Mobile App, anything you are solving, make sure you are under the time pressure.