More than half the students that you generally meet have really not begun their IIT JEE preparations in full swing. Most of them are half stuck in either Rotational or in Gravitation. In Mathematics, they are really not well prepared. Either they have just finished most of AP, GP and HP or have just done some differentiation. In Chemistry things are generally better but then still not up to the mark. 

If you happen to be one of these then this is very important for you. The first and foremost thing is to start realizing that Mechanics alone will take you no where! You have to start working on Electrostatics, Current Electricity, Modern Physics, Optics, Heat and thermodynamics and the other simpler topics. They are the marks scoring topics for JEE. You should also realize that the summer vacations are the most curtail time for you to cover the backlog you may have created. You should try and study Integration. Lot of students tend to miss out Physics because they don't know integration. The part of integration needed in Physics is not very tough but it is important tat as soon as you come to class xii you are able to understand integration. The school syllabus for Mathematics is generally sufficient for preliminary Mathematics. 

One more thing which is very essential, The boards exams will be due near your IIT JEE entrance examination. It is very important that you realize that a period of one month will get lost due to board exams, pre boards and practicals. So you have to make sure that you make up for that lost time by not losing time straight away. 
By now, you already have a rough or clear idea of what the syllabus is and what the topics are, the things that are your stronghold and others that are your weak points. You have to dedicate time accordingly. You should always remember that you can improve most in the subject which you are weakest at. 

One year is generally a lot of time. It is a myth and an agenda sponsored by coaching institutes that IIT JEE cannot be cracked in 1 year. IIT JEE is not for Extraordinary people. You fit in the league and you have to believe in your abilities. You have to benchmark yourself with the best and give it your best at times.