Konnichiwa is the main, more formal term for greeting. This is the term you use for respectful meetings. (Practice the pronunciation.) There are quite a few other terms. Ohayo is a lot less formal but works. It's basically a 'good day.' Another way of saying it is "Ohayo Gozaimasu," which, again, is more polite and formal. When saying gozaimasu, the 'u' is silent.