I just watched the 2002 film version of
The Importance of Being Earnest, which is one of the cleverest plays I've ever seen. It got me thinking about the particular group of period-piece comedies into which it falls. Other stories in this group include Gilbert and Sullivan's works, Moliere's The Miser, most Shakespeare comedies, a lot of Saki's short stories, some O Henry stories, and anything written by PG Wodehouse.
Within this group, there are a lot of similar themes and elements. I've figured out several lists detailing them.
Story elements:
Bets
Blackmail
Duels
Family pride
Love triangles
Matchmaking
Mis-mailed letter(s)
Mistaken identity
New-found inheritance
Political corruption
Social Hierarchy
Relationships:
Two relationships can be given per character, so that the second can be revealed in order to move the plot along during the 2nd or 3rd act.
Aunt/Uncle
-overbearing, doting, cool
Boss
Butler
Cousin
Father/Mother
-step-, foster
Fiancée
-secret, arranged, normal
Friend
Husband/wife
Nanny
Old military buddy
Old school chum
An optional list is that of the possible supernatural elements. These change the nature of the story, making it even less realistic than it already was, so they should be handled with care. Also, it's a short list, since there aren't many supernatural things that constantly come up in witty comedies.
Supernatural Elements:
Deities
-benevolent, malevolent, pranking
Ghosts
-advice-dispensing, task-requiring
Love potions
My last list is of the elements that are more or less completely essential to this type of story. I saved it for last because these ones are pretty intuitive, and shouldn't need as much attention as the others when one constructs the story. They're just helpful to have in mind.
Essentials:
Intellectual exchanges of wit
Lies
A happy ending
Using these lists, one can compose a plot. Mix and match three or four story elements, pick out some good relationships for the characters, and then make a plot that works off of each one. If one can make most of the plot elements intertwine with each other, it will work well.
A good technique is to choose one of the story elements to center the entire plot on, and weave the others around it, since this makes the story cohesive. Give the characters unrealistic priories, like family pride or a bet over one's life, since this opens up a lot of story possibilities that wouldn't actually exist in real life, and makes the story funnier.
You'll have to come up with the wit by yourself. Originality is one thing I can't help you with.