Hello Disha, to get a good score in KCET 2019, just follow some preparation tips.

1) Make a study plan
This will keep you organised, ensuring that you don't panic at the end.
2) Revision
Revise what you read, that's the key to learning such a vast syllabus.
3) Practice
You must practice as many previous year's questions as you can. It will increase your speed as well as give you better results in the exam.
4) Don't Panic, stay motivated
The more calm you are, better for you. Because then, you can understand the concepts more thoroughly and stay refreshed throughout the day.

Best books for KCET 2019
1) Text books of Class 11 and 12 for Chemistry, Physics, Mathematics - NCERT
2) Karnataka CET Engineering Entrance 16 Year's Solved Papers - Arihant Publication
3) Karnataka CET Explorer Engineering - MTG Editorial board
4) Pradeep’s Fundamental Physics (Class 11 and 12) - K. L. Gomber and K. L. Gogia
5) Modern’s Abc of Chemistry, Part 1 and part 2 - S.P. Jauhar

You can get Important topics for Physics, Mathematics and Chemistry for KCET 2019 from the link given below:
https://www.google.com/amp/s/engineering.careers360.com/articles/kcet-2019/amp

Also, do refer the syllabus once. It will help you a lot.

All the best!
I hope this helps.