What should be my strategy to crack the BITSAT 2017 ? And what will be a safe score for getting into Computer Science or Chemical branch ??

Don't waste time solving lengthier questions, but root for questions which are more concept based. You must have all formulas and equations (algebraic and chemical alike) on your fingertips. Know that almost seventy percent of the question paper is formula based. The most important out of all the BITSAT tips and tricks is and most efficient is time management. Only those who are able to solve questions accurately and quickly are the ones who grab the baton. You can divide your time for separate questions. BITSAT is online test. So, solve online test series as much you can. You can check the BITSAT cut off for different branches through the below link- http://bitsadmission.com/cutoffscores.aspx