We don't know much about Mycenaean beauty standards, as most of their writings revolve around record keeping and trade rather than literary works, news reporting, or other types of writing. The script of the Mycenaean Greeks, Linear B, was not very good at encoding Greek. It was successful as a script because the limited nature of employment of Linear B (in addition to experience/training and context) allowed scribes to understand what was being written, despite the origins of the script obviously being tied to another language. In short, you're not going to find an epic poem like the Iliad written in Linear B.

Our best bet at answering your question will probably be by looking at the art of the Mycenaeans and how they depicted themselves. The Mycenaeans painted beautiful frescoes, such as this one from the acropolis of Mycenae (ca. 13th century BC). Women are often depicted wearing colorful dresses and with their breasts exposed, quite different from the chiton or peplos that we usually imagine ancient Greek women wearing. We've also found artifacts like this, which depict the face of a woman, possibly with makeup.