Jane Austen's characterizations, including character descriptions, are often very indirect and spread throughout the text, therefore, they can be difficult for a first-time reader to pinpoint. Austen never goes into very detailed descriptions. We don't know what many of the characters look like beyond level of attractiveness and even height. We don't know hair color, eye color, gown color, etc.
That being said, we first learn that Jane is the handsomest, or prettiest daughter in the family in the first chapter, when Mrs. Bennet declares that Lizzy is not "half so handsome as Jane, nor half so good humoured as Lydia" (Ch. 1, Vol. 1). The next allusion we get to Jane's beauty is at the Meryton ball when we hear Bingley proclaim to Darcy that Jane "is the most beautiful creature I ever beheld"(Ch. 3, Vol. 1).
Likewise, we never get a detailed description of Caroline Bingley. When we first meet the Bingley party at the Meryton ball, we learn that both of "his sisters were fine women, with an air of decided fashion," meaning that they were very noble, genteel women, who were very richly and fashionably dressed (Ch. 3, Vol.1). When Elizabeth stays at Netherfield to be with her sick sister, we learn that Caroline Bingley has a very attractive figure. Caroline is walking up and down the room to get Darcy to notice her and the narrator states that "her figure was elegant, and she walked well" (Ch. 11, Vol. 1).
We do not learn much about Charlotte Lucas' looks until Mr. Collins proposes to her. When her parents agree to the marriage, we learn that she is 27 years old, and "without having ever been handsome." In other words, Charlotte is quite plain, getting older, and in danger of becoming an old maid (Ch. 22, Vol. 1).