what words should an invitation letter carry?

I'm a student, my brother is studying in Australia and he got Chinese tourist visa from there, so I want to visit China with him. My brother got the visa by the invitation from his Chinese friend. So, am I going to get a tourist visa to visit with my brother if his Chinese friend send me invitation? as his Chinese friend is known to me and I've also visited Australia before. If his invitation letter is acceptable then what things he should write on the invitation letter to invite me to get a Chinese visa. I'm very eager to visit China so please help me.
Thank you.