In order to get 230+ in JEE 2019 you should focus on chemistry because it is least time consuming and scoring as well, if you have a strong command on each and every topic of chemistry you can even score 100 around marks in chemistry only and to achieve a good command you should go through ncert thoroughly and practice from books like Narendra Awasthi (for physical chemistry) and MS Chouhan( for organic chemistry). Now despite of chemistry for mathematics and physics you should practice 38 years solved IIT papers thoroughly, as jee mains is all about speed and accuracy. And now if you have time you can go with books like DC Pandey for physics. I hope my opinion will be helpful for you .