No IIT does not need any preparations from 10th class. It's better to focus on board exam at that time because that 10th class percentage matters a lot throughout the life.
Start preparing from 11th class. This starting time of 11tg class is very essential because right from starting basic fundamental things are taught which students generally don't pay attention very much and miss them which cause a lot of problem while learning the advanced things in all the 3 subjects i.e. physics, chemistry and Maths.
So if you keep yourself regularly updated with whatever has veen taught in schools and coachings. Plus keep on solving questions because learning theory is not sufficient to clear IIT-JEE right from 11th class starting to 12th class end consistently then you can definitely crack the IIT-JEE.
