The first thing that jumps out to me is that you need to spend a good amount of time reviewing and practicing the basics ( something I had to do as well). A couple of books to help you with that are the
MGMAT books and also the Kaplan Math Workbook. Knowing the basics enables you to build a good foundation. Then, start off working the easy problems in the OG an work your way up in terms of difficulty. That's the path that I've followed and has worked great for me. Also, don't forget to keep an
error log so you know which concepts you need to review again. I've recently started using flash cards and it's working good for me.
Good Luck!