what are the best website for practice the sample paper for iit jee main and advance-2019.

IIT JEE 2019 (JEE Main + JEE Advanced Preparation Strategy)

For IIT JEE preparation, if you have not done yet, Start loving Physics, Chemistry, and Mathematics!
Concepts and Practice for JEE Advanced. Speed and Accuracy for JEE Main. If you are JEE aspirant focus on all 4 : Concepts, Practice, Speed, Accuracy.
It is important that your basics of almost all the topics are clear and that you can tackle easy or moderate level problems in those topics, because sometimes easier questions may come from the topics which you didn’t prepare that well.
Prepare a timetable giving time to all the subjects. Do not neglect any subject or give excessive time to any subject.
Practice a lot. Never Ever Look at Examples or Read them. Practice every time. Though everything appears simple, never let the book solve a question for you.
After Solving a Question One should start evaluating himself in terms of Speed, Line of thought (thought process) and Accuracy. (Right method for practicing and preparing for JEE).
Solve as much as you can, increase your speed and accuracy, and the most important thing is, get your doubts cleared from your teachers; do not keep them pending and piling up.

Things to avoid in IIT JEE 2019 preparation

Procrastination: Avoid backlogs. Clear your doubts asap.
Excessive TV/Social media: Avoid anything that can take your precious time, JEE need your focus and dedication, rest of the things can wait.
Quantity over Quality: Quality matters more than quantity in JEE. The number of books you read is not proportional to your chances of success in JEE. You need to aware of what’s in the syllabus and avoid questions which are above JEE level.
Become sad due to low scores in tests. JEE preparation is a journey. You will improve with each test. Monthly tests/Practice tests are just to analyse your understanding and learning. It’s a way to learn from your mistakes.

If u need websites, U can try for ask iitians and embibe but what is more important is self study. Best of luck.