Will it be weird if I mailed Graduate admission office or any Professor for detailed information about their program quite early, as in junior year, so that I can best prepare myself for that particular program. I’m talking about one or two programs that I really want to get into. I’m a EE engineering student.
Unless you are looking to volunteer in their lab next summer, you should wait until you have an application in to their program. You are likely to get a better response when they consider you as a potential group member. As for the admission office, there is no point unless you are applying.
Also, what kind of detailed information would you ask for? Usually everything you need to know about the program on a basic level is on the website. It would make you look bad if you asked for information that is readily available on the website.
The preparation that you would do for one or two programs is the same as the prep for any other program - you need research experience, high grades and test scores, excellent letters of recommendation, and an outstanding statement of purpose. You also need to be a good research fit with the department. Generally speaking, you want to select departments that fit your interests - not try to tailor your interests to get into specific departments. But even if you wanted to know research of the current faculty…that information is also on the website.