The universal way for preparing any Competitive exam is that, your basics of Higher Secondary is clear if you're basics are clear you can attempt very good marks in any Competitive exam. Work on your Physics, theorem & derivation practice Math's daily, learn chemistry's reaction (named reaction) and you're all set for exam.

The result of this examination GUJCET is different for every categories. Candidates who are belonging from general category should score at least 130 marks out of 300 in theory part to be eligible for GUJCET Examination. This is the minimum marks but it varies for different colleges. There are three rounds of counselling in every colleges.

Visit this for more information,

https://engineering.careers360.com/articles/gujcet-cutoff

I hope my answer helps. All the very best for your future endeavors!