My son is studying in 8th Std. in DPS school in singapore , he will be promated to class IX , how to prepare for IIT JEE exams in siangpore from class IX sothat he can have more time to plan & execute in better way.

Your son is only in 9th standard so you need not to worry that much. What he needs to do is to concentrate on his school's syllabus books of science and maths conceptually. He can refer some side books like Maths by RD Sharma and Pradeep's Publications Science books and He must try to solve general brain teasing questions. HE may refer newspapers like Times of India to solve Brain Strain questions.He can also join Online or postal coarses as such Kayson's education. Really He needs nothing else than this untill he passes 10th standard. And after that he must start reading IIT-JEE preparation books. And If possible join a better coaching institute.