You have to maintain CGPA minimum above 8.5. Prepare for GRE from famous websites like Magoosh, princeton etc., you have to score more than 325 to go into stanford. you have to make two documents called SOP(Statement of purpose), LOR(letter of Recommendation) both have to be very attractive and effective. SOP means why you want emdedded systems in stanford university and LOR has to be written by someone who has any PHDs related to Embedded systems or someone who did some research on that topic. It is better if the person has some good name and image. It is better if u do some projects on embedded systems and write some research paper on embedded systems. After GRE you have to write IELTS/TOEFL , for IELTS 7.0 is minimum score required and for GRE 100 is minimum score required.

All the best!