It would be good if you could share what is your current preparation status but in order to get good score below provided general tips would be good -

1. Know the syllabus very well.
2. Read standard books only as there are many books available in the market so it is advisable to use the books which make all your concepts clear and which are easy to understand.
3. Understand the weightage of topics properly and devote time accordingly.
4. Proper Revision plan should be followed.
5. Mock Tests and Practice Tests should be done as this will help you to learn time management skills and this will also make you familiar with the exam pattern.

Also, to check the complete preparation strategies for Gate CE you can go through the below link -

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

And to check NITs/IITs cut off you can go through the below link -

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

Good Luck!!!