Biotechnology

There are two things –
One, you want to clear GATE and second you want to score a good rank. For No.1, just Study for a month from any Xyz BT book.
For No. 2, you have to follow a long and laborious path, I think 6-8 months are necessary for GATE prep. Just make proper time schedules, undertake regular test and study regularly
Now coming to the books
The wonder and magic book - Biotechnology a problem approach by pathfinder academy (don't make a mistake to overlook this book.)
The above book is though sufficient in many ways but to score a rank of 30 or less from a rank of 200, you need to carry extra. Alongside pathfinder read standard book of every subject i.e. Kuby, Prescott, t a brown, Doran, Shuler, Whittaker, Alberts and all the standard books of subjects that you have read in these 4 years of engineering. The other books that you would require is Maths, sample paper and previous year solved question books of pathfinder academy. Believe me these would be sufficient and it might sound much but once you start preparing through them, they would become doable and necessary. All the Best.