If you are preparing for JEE main fromthe past or  for class 12th board from the past few month on a serious note and right now you want to start preparation for the advance then yours it is the right time to start preparation for the JEE advanced and in fact it is the case because you are asking for the advance so perhaps I believe that you are well aware of JEE main syllabus and are able to score the qualifying marks.

You can use the following strategy to score good marks and crack JEE advanced

1. Always remember the syllabus and it is one of the key to success because if you are taking to the syllabus then you can give lot of times to the content which is relevant for the exam in state of going out of the syllabus.
2. start preparing from the previous year question because it is the fact that you are going to face the similar kind of question in the JEE advanced.
3. practice is the key to success and your practice does not mean that solving the same question again and again but instead go for some new question because jee advance ask for out of the box thinking
4. when you are preparing for the exam keep in mind that some topics very high voltage compared to others for instance in case of physics you need to focus more on rotational motion electrostatics and modern physics in case of chemistry if you are good at organic chemistry then interested all the mechanism because the question will be from the mechanism and not directly.

Just follow the above mentioned tips and don't lose hope till any. To get success in the exam