I'm gay, so I feel like I can answer this question
What makes a guy "cute" in my opinion is either looks (a bit muscular but handsome in the face = cute), or the way he acts. There was this one guy who I thought was the cutest guy ever. He was my height, he was gentle, he made a lot of small jokes and he was a bit to himself but friendly. That's what made him cute - that and he had a bit of a mustache like me n.n
So what really makes a guy cute is both his looks and his personality.
That's my take on it, although other girls and guys might look at it differently. Although I agree with Fallstel and Anthony - just be you, and you'll have a much better relationship because she likes you for who you are =]