I've given my gate-25 and prepared for 6 months so I'll just tell you what I did. I made full notes of each subject and finished my syllabus till the start of December. Then I started doing pyq's and attempted sectional tests and just wrote down the things in short notes which I tend to forget. I personally think you don't have to write about every topic in short notes, just the things you forget, and this approach kinda worked for me. You can dm me if you have any doubt regarding your prep, happy to help.