I utilized
Manhattan GMAT's online class called Interact to learn the base of material for both quant and verbal. It was very, very helpful building this base set of knowledge, the strategy guides in particular are great. However, after a few months and testing around 710, I was still ~60th percentile on quant. I didn't really know what to do from there, doing lots of random questions wasn't helping. Finally, a friend recommended
Target Test Prep for quant and it was unbelievable. They teach you the material by drilling a lot of questions on each particular topic until you understand it. The lessons are very clear and the interface is great.
Honestly, 100% the key to me moving up my score was starting the
Target Test Prep program. It took a lot of work, but after about 2 months of doing the
Target Test Prep quick lesson and a ton of chapter tests and custom tests, I broke through and ended around 80th percentile with a 760 overall score and 8 on IR.
Studying for this took a ton of time and work, put in the effort and stick with it! Good luck!