My idea would be to describe how characters react to them. If everybody is chasing a character around, that would indicate she is pretty.
In one story I wrote, the narrator was describing her mother as "looking like an actress on a safari", thereby hinting that she was pretty, she was dressed in a certain manner, that there was some sort of connection with Africa in my story, and the character's pride in inheriting her mother's good looks. Of course, this narrator also happens to know her genetic pedigree going back to the 14th Century, and happens to be the target of a white supremist leader who wants her to become the mother of a master race, so readers would probably guess that she is good looking.
I tend to be of the school to let the readers form their own vision of the character, and if different readers have different visions, that's alright. So I might mention beauty if it is a story point, such as one character who is a porn star, so discussion of her body parts was in keeping with that persona.
Whether good looking or not, I'll try to keep in mind who is looking at the character. In one story idea I have, the POV character is a detective, so he is going to notice her muscular arms and the callouses on her hands that indicate she's a serious martial artist. In another story I did write, the guy noticed her curvacious curves and round breasts and mane of hair flowing down her back, and her green skin which, in his opinion, was a definite showstopper. In yet another story, the fact that the female character was wanted by both the hero and the villain, the latter spending a scene watching her as she prepared dinner for herself and the hero, indicates that she is kind of hot, as well as the villain's thought that, she's kind of hot.