I cracked the IIT-JEE in my first attempt back in 1998 and secured an all-India rank of 713 (general category). I guess that qualifies me to advise wannabe IIT grads.
I will begin with some general advice. One very important factor for achieving success is focus. That means maximum time and effort should go into preparing for IIT-JEE. Board exams cannot be top priority. Nor can be any other engineering entrance exam. If you want to be a B.Tech. from an IIT, then you HAVE to make the IIT-JEE top priority. And forget about any taking medical entrance exams. As they say, it is not wise to keep two feet on two different boats.
Now, I will deal with each subject separately. Of course, before that, an important caveat: know your syllabus. Do not waste any time on material that is out of syllabus. Why on earth would you, huh?
Let’s tackle Physics first. The textbooks that one should follow are HC Verma and Resnick & Halliday. Unless you are exceptionally bright, it is not a bright idea to start attempting problems from Irodov right away. You will not be able to make head or tail of them and will just be wasting time. Attempt the problems of HC Verma for a start. It has a set of problems that are of adequate difficulty and attempting them will keep paying good dividend, even at the end of your preparation. Get the material from Brilliant Tutorials and solve the given assignments regularly. After some time, switch over to Irodov. You could do this, say, 6 months after the beginning of your 2-year preparation-span.
We shall move on to Maths now. Start off with the textbook prescribed for your board. The next stage, which you can start about 2-3 months after day 0, consists of attempting ML Khanna and assignments from Brilliant Tutorials. After about 6-7 months, you should purchase your copy of TMH (Tata-McGraw Hill) for Math.
Last but not the least, we come to Chemistry. This was most scoring for me and it could be for you too. RC Mukherjee contains a good collection of numericals on Physical Chemistry. OP Agarwal’s book is worth a buy. It covers the entire syllabus on chemistry comprehensively. You can read Morrison and Boyd for some fundas on Organic Chemistry but be careful not to venture out of syllabus (because this book reads like a story).
Now, for some more general tips. Judiciously choose a group of friends who want to crack the IIT-JEE. This peer group will keep you well abreast of the goings-on that you need to know about. Like for example, some book from a new author could perhaps be a better buy than the books I have mentioned above. Of course, do not fall into the trap of collecting too much extra material and then be at a loss what to do with all of it.
Best of luck...