友達になってください

As far as I mde experiences in Japan, there is nothing like an easy "let's be friends" in Japan: you belong to the same company or sports club or the like and get acquainted because of that. One big hindrance for you will remain: you are not Japanese. In the end, it all depends on what you expect of becoming friends with a Japanese.

友達になってください is more like "Please be my friend", which sounds polite. If you want to be intimate, I think maybe 友達になろう is better.