"I'm looking great, and how are you doing?"
Let's break it down:
* Estoy buenisima: This literally means "I am very good" but it's often used colloquially to mean "I'm looking great", "I'm feeling fantastic", or "I'm hot".
* Y tu: This means "And you?"
* Como andas: This is a common way to ask "How are you?" or "How are you doing?".
The phrase is typically used in a playful or flirty context, especially if the person is looking for attention or compliments.