Using the Familiar
Many sketch comedy shows focus on current social and political trends -- just think of the famous television comics who do their impressions of presidents and rock stars. If you're not great at impressions, you can still write a skit that incorporates things that are familiar to most people, everything from shopping at the grocery to the poor quality of airline food to a random news event or social observation. Some ideas: two sisters who try to outdo each other in caring for their pets, two teenagers complaining about how people are addicted to electronic devices, or a man trying to explain the concept of God to an inquisitive 6 year old.
One surefire comic technique for writing funny skits is putting unlike things together for effect. For example, transport a conservative soccer mom to a hippie yoga class. Place a vegan smack in the middle of a cattleman's convention. Put a tone-deaf singer in the finals of a vocal competition. Put a cheerleader at a funeral. Putting unlike things together, or juxtaposition, is one of the most often-used techniques in skit writing.
One popular and easy-to-do skit idea is to use an existing format (a television news program, a cooking infomercial, a soap opera) and tweak it to fit the circumstance of the skit. For example, if you work for a hospital, parody a gourmet cooking show featuring things like jello and unidentifiable beef dishes. Or, if you're a teacher, host an episode of "Cribs" where you give people a tour of your no-doubt humble abode.
Some skits use wordplay as a way to convey humor. Choosing one word that is confused for another in the context of the skit can be milked for laughs, although it can get old pretty quickly. Often, these wordplay skits are off-color, so if the audience is fairly conservative, this type of skit can be tougher to pull off. One example of this type of skit is the Betty White Delicious Dish sketch on Saturday Night Live. Ideas for this type of sketch: the seven dwarves in group therapy discussing their new names, which are contemporary problems (Wimpy, Sleazy, Jumpy) or a twist on the old Red Riding Hood fairy tale, Little Red in the Hood, set in a gang-infested neighborhood.