First things first.
Score atleast 60℅ in each of PCM, and an aggregate of atleast 75℅ in your boards.
Then, prepare for Jee advanced as best as you can, and give all of the mock tests in less time as I compared to JEE mains and advanced, depending on the type of tests you are giving.
But please, first have your concepts really good.
Fill the BITSAT form (They are out now), and fill it correctly. Also, don’t forget to fill the test centre preference, because it is filled separately, after Mains I guess. So keep hunting.
Then you are good to go.
But here’s a little piece if advice you may find useful.