My suggestion is don't begin your math prep from OG or any other study material (kaplan
I began my maths prep by taking a diagnostic test, so as to realise my strengths and weaknesses. Initially I was not comfortable with premutation- combination and number system problems. I took help of some elementary books on mathematics, and praticed many questions on these two topics.
I will advise you not to memorise anything other than formulaes of geometry, and if you have any problem remembering them just make a chart of all the formulaes and hang it on the wall and just give a look to it whenever u wish.
In my opinion if one knows trignometric ratios ( values of sine, cosine, and tangent from 0-90) and some basic formulas of coordinate geometry it will certainly help.
Moreover, I won't suggest anyone to use number fitting approach as suggested by kaplan
. It is always better to solve the questions in conventional manner.
If you have anyother query or any problem in any topic, you can write to me.