Dear Niladri,

There is nothing called passing marks in NEET Exam. In NEET, it is qualifying marks rather which is 50th percentile for general category and 40th percentile for reserved categories. Try to score 550+. Then you'll definitely get a good medical college.
If you want to score good marks in NEET then just follow simple steps -
Clear your basic concepts.
Be thorough with NCERT textbook. Its a must.
Solve previous year question papers.
Take mock tests to assess your progress.
Solve questions from any reference book you prefer for competitive exams
Solve as much as numerical possible.
Use shortcuts to solve to save your time. Formulas to be at your Fingertips.
All the best !