IIT

After JEE Advanced, the procedure is quite simple! Just wait for the results to come. Once the results are out, there will befilling up of choices online. Then comes the mock seat allocation, in this process you will get to know which seat you will get according to your preferences. Then you will have 1 day time to change your choices if you want. Then the first round seat allocation takes place. Now comes the main part, document verification. You need to go to the nearest IIT and get your documents verified. If all your documents are verified, then your seat will be confirmed. Congrats.
The procedure is same for NITs too. Hope this answers your question. For further information and the schedule, follow this link, choose your options appropriately. Verify your position based on previous year cutoffs and assess accordingly. Mock seat allocation.

JEE Main Preparation
Tip 1: Be Focused
First of all, you should be mentally prepared and keep a positive approach towards your goal. With the really high levels of competition and peer pressures, it is very easy to get distracted and doubt your methods of preparation. It is important to just focus on your preparation and believe in yourself and your methods. Since JEE Main preparations can be very intense, it is very important to be ready to put in all the mental and physical effort required to clear the exam.
JEE Main Preparation Tip 2: Have a Preparation Strategy
Being organized is one of the cardinal factors that make a difference when the result comes. For a highly competitive exam like JEE Main, without a proper preparation strategy in place, winning will be little difficult if not all that impossible. Also, pay attention while making the exam preparation strategy. Prefer allocating more time to subjects and topics you are weak in. Following the preparation strategy to the core is also essential to score higher in the exam.
JEE Main Preparation Tip 3: Use relevant study material.
You should know the entire syllabus that will be covered in the exam; so that you can collect study material for preparation. Reference tobest JEE Main preparation booksandprevious years question papers for JEE Mainwill go a long way up into your preparations. Although it is said that NCERT syllabus is sufficient to clear the JEE Main exams, students who appeared for the JEE Main 2017 exams felt that reference to other JEE preparation was a must to clear the exam and only NCERT was not enough.
JEE Main Preparation Tip 4:Time Management
Following a strict timetable as per specific syllabus and targets is very important if you want to complete the syllabus on time and also leave ample amount of time for revision. JEE Main preparation must also include solving sample papers, previous year's JEE Main papers. To save time during revision, you should make notes of topics while preparing them, so that during revision you don't waste too much time revisiting each chapter and instead you can refer to the notes. Solve more and more problems, discover more and more new tricks.