JEE Main 2017 answer keys were released recently and by now students who appeared in the exam would have a fair idea about their marks in the exam. Also, they would by now know if they would be eligible to sit in the JEE Advanced exam. Just to jog our memory, as per the official notification candidates who are in top 220000 of JEE Main are eligible to appear in JEE Advanced. So candidates who are confident of making the cut, should know that even though JEE Advanced is some sort of succession of JEE Main, both exams are different in many aspects.
First and foremost, the difficulty level for JEE Advanced is a notch higher than JEE Main. While for JEE Main class 11 and class 12 textbooks are enough to get a decent score and rank, in case of JEE Advanced you cannot just rely on school textbooks and would need an extra edge.
For long, toppers of JEE Main have agreed that focusing on the school textbooks are enough for the exam. In case of JEE advanced, though questions are not directly from the textbooks and are generally concept-based, which means it is not adequate to know the concepts but you should also know how to apply concepts.
JEE Advanced has a similar pattern to JEE Main but instead of asking questions about concepts and theories, JEE Advanced questions focus more on testing your ability to apply the concepts and theories learned to practice-based questions. None of the questions asked in JEE Advanced are from outside an NCERT textbook (usually) but students find it tricky if not in the habit of solving application-based questions. JEE Advanced questions are more like a version of the High Order Thinking Skill (HOTS) questions which are asked in CBSE board exams.