Some elements that can help analyze tone are diction, details, imagery, and sentence structure. When Austen is describing something that she particularly feels is ridiculous, such as Mr. Collins, we can pick up on subtle changes in these elements. While we are limited in space and can't go into detail about all of the above here, below are a couple of ideas to get you started.
Diction specifically refers to an author's choice of words. Words have connotations as well as literal meanings, and every word is chosen with care and intention. One word we see Austen using in her description of Mr. Collins is eloquent. In particular, when he is dining for the first time at Longbourn, after dinner, Mr. Bennet attempts to make conversation with him by asking him about Lady Catherine de Bourgh. Austen then describes Mr. Collins as being "eloquent in her praise" (Ch. 14). Though a reader might miss it at first, this phrase and word particularly smacks of sarcasm because, not only is it ridiculous of Mr. Collins to carry on about Lady Catherine as he does, we later see that there really is little about Lady Catherine that is worthy of being praised. She represents the characteristic noble class that Austen is criticizing in the book. She is prideful, condescending, and treats individuals as lesser people, such as Elizabeth even though she is a gentleman's daughter simply because she has working class relations. The only other place we see Austen use the word eloquent is in her description of Darcy's first proposal. Austen relays that Darcy was "not more eloquent on the subject of tenderness than of pride," meaning that he spoke less about the nature of his feelings and more about the fact that his feelings degrade his pride since Elizabeth is considered beneath him due to her working class relations, even though she herself is a gentleman's daughter (Ch. 34). Here again we can hear the sarcasm of her tone because wounded pride clearly is not something one should be eloquent about, or dwell on for any length of time, when offering marriage.
The details Austen relays in her characterization of Mr. Collins also clearly reveal her tone. For example, after Mr. Collins praises the fact that Lady Catherine approved of all of the changes he has made to his new parish home, Hunsford, he also praises the fact that she suggested changes of her own. In particular, Austen points out that Lady Catherine suggested adding "some shelves in the closets up stairs" (Ch. 14). This may be a very subtle allusion to a reader who is unfamiliar with the culture; however, the reader might notice that the punctuation Austen chose to use signifies the comment's importance. She uses dashes to set it apart, plus it is the last phrase in this paragraph describing Mr. Collins's exuberance over Lady Catherine. Once the reader has noticed the phrase's importance, one can then consider that those closets refer to bedroom closets, and that putting shelves in a bedroom closet is an absolutely ridiculous idea because it leaves the ladies with absolutely no place to hang their gowns. Hence, this one subtle detail does a lot to set the tone and to paint both Mr. Collins and Lady Catherine as absolutely ridiculous people.