The greatest problem with the quantitative reasoning section is without a doubt the time pressure. One of the ways to tackle this is to be able to quickly ascertain which questions will take too much of your time and knowing when to leave them out. You can also improve your quick arithmetic skills by doing practice questions and even puzzles like sudokus! With this section the most important thing is not to panic and to be able to quickly power through the easy questions. The questions you leave will be flagged at the end and you can even leave a marker on questions if you have absolutely no idea so that you don't waste time when reviewing at the end.