Before going to start your preparation you must know the syllabus of the AMCAT exam . Then according to the syllbus set the target . Read the NCERT book thoroughly then move to the mock tests which are available on many of the sites..
Lets break it section wise :
Quant : For Amcat you can solve Arun sharma till LOD 1, But it would be preferable if you extend your practice to LOD 2 so that you can get good score in Elitmus exam too.
Reasoning : Practice from Arun sharma logical reasoning and data interpretation book or you can solve RS Aggarwal . I would suggest solving arun sharma rest is your personal choice.
Verbal: This is easiest section of all you can practice from Arun sharma or any other publications book.
Computer Skills/Programming : For this section you can refer websites like Youth4work. Only questions of basic level are asked in this section.
Domian Knowledge: Youth4work app/site is good for practice of this section and you can revise your concepts from your college books/material...