Hey
SenpapiGMAT Quant is not so much about learning the concepts but the application of these concepts.
I would recommend you to follow the theory you study using the Manhattan strategy guides
with some practice specific to the topic. If you have the time, try and supplement the concepts
you study from the Manhattan guides with the
GMATClub Quantitative Mega-thread.
This thread will help you reinforce the concepts you have already done once.
Try to understand if you are able to apply the learning to the problems. Every time you are not
able to solve a question go through the thread(where this question has been discussed) and try
to learn from the various methods given. You may come across a few methods which might
help you save some time.
Last but not the least, work on maintaining an
error log and go through the mistakes you make
from time to time. This will help you eliminate the mistakes you make on a regular basis and
help improve your scores.
Hope this helps you!