You can check out takshzila shikshak's videos on YouTube and free funds books to form your basics of TSD. You should practice from CL and takshzila books to form the aptitude to solve questions
For me, solving questions from Sarvesh Verma and TIME material helped a lot as they provide plenty of questions on every concept. You can refer to them for improvement.
For TSD, look at the formulas and also the derivation of them
Start by simple problems and understand how to solve them using 2-3 different approaches, especially the ratio approach
Now, practice all TSD questions that appeared in CAT for all the previous years
This should help since arithmetic is a very important section for CAT