If you are preparing for GATE 2023, then the first thing you should know is about the syllabus of GATE. So you can download the syllabus of GATE 2022 and start preparing based on that, because usally the syllabus won't change a much.

Now after you know the syllabus, the thing is you should start clearing those topics out from the books you have in your UG course. Now along with it, it would be better a choice for you to practice problems from the books by Pearson for GATE 2023 which have previous year problems. So studying the topics and practicing problem is the thing you must focus on till the Month of November,2022 as by then you should have completed the GATE syllabus. Now the last two months i.e., from Dec'22 to Jan'23 end you should revise and practice mock tests.

Also while you are studying topics create notes which you will revise through. Make it as brief as possible and it must contain all the important formulaes in the topic.

For the important topics you can consider visiting the link below:

https://engineering.careers360.com/articles/how-prepare-for-gate-chemical-engineering

I hope this helps. Wish you a great day!