Hi!
I would suggest you to first pick a topic which you are comfortable with maybe geometry, number system, algebra anything. Lets say you chose geometry,
1. Read the theory (you can read it from publication you are comfortable with could be the theory in OG or GMAT Club maths book or manhattan) but make sure to jot down all the concepts that you come across (by all the concepts I mean those points which you can quickly refer to)
2. Do not start solving with questions from OG. Start from problem solving from other "good" sources and filter for sub 600 problems and then gradually move to problem of higher difficulty and solving data sufficiency as well.
This would surely take time but it helps!
Once you are confident enough, you can then start solving from OG, OG helps you to understand the way GMAC can formulate a question and this would be helpful if you have a strong foundation.
Thanks!