劳伦 (láo lún)
This pronunciation is fairly close to the English pronunciation.
Here are some other options, depending on the context:
* 罗伦 (luó lún): This uses a different pinyin spelling, but sounds very similar.
* 莉莲 (lì lián): This is a common Chinese name that sounds similar to "Lauren" and might be used for a more "Chinese" feel.
Ultimately, the best way to say "Lauren" in Mandarin Chinese is to choose the pronunciation that you feel comfortable with and that is most appropriate for the situation.