Preparation for entrance in BTech college first year is that you need to be clear with your all doubts of class 11th and 12th thoroughly. You have to give JEE mains paper for entrance in BTech aur your selection could be on the basis of 12th percentage in any board. After clearing all your queries all ,your doubts and having all information about the basic chapters like trigonometry , conic section, vector ,Matrix , determinant you can make your maths good for entrance exam. Solving your questions, solving different type of problems can make your maths good.
I hope your doubt is cleared.
All the best for your future!