You first get the chapters and theories cleared from your regular books from NCERT or the ones you use for preparing JEE.After this, you can solve BITSAT practice questions and Archived questions from Self Study Guide for Online BITSAT Book by Arihant.  

For your inchancement in speed and accuracy ,it would be better if you solve the questions alongwith time limit. Like there are 20 archived questions in a chapter, set 20 minutes timer and then see how many you were unable to attempt and in how many you did mistake. Work accordingly then.

After completing syllabus, do give mock tests..lots of mock tests. There are 5-10 mock tests and previous year paper in the book and a cd provided with it. You can also use Embibe to give tests.

All the very best.