Practice for Quants - how do I go about it?

I would recommend using a source where the questions are in some sort of increasing difficulty. I would recommend using the Official Guide Quantitative Review 2nd Edition, there are about 300 Quant questions. It is possible that even after reviewing the concepts you are not ready for the question bank, or perhaps the question bank is harder than where you are in your preparation. If you use the OG 2nd Review you will be able to see where your mistakes percentage is starting to go up. If that happens, let's say at a third of the way then you are still not strong in a lot of the concepts and the additional practice will help you strengthen those. This is what I would recommend. Practicing with content that is significantly above your current level can be counter productive. The best is to stage the difficulty level of the content.