Hey dear, it is good to see you eager for preparation for indian army. I want to tell you that if you want to prepare after class 8th so you must take admission in some sainik school like RIMC, ghodakhal e.t.c, they are mainly officers making machines with success rate of almost 80%. So, you dont need coaching so early if you can join a proper school for you goal. Although, if you are comfortable with coaching than i would recommend you Baalnoi Academy in janakpuri, delhi.