Things You Will Need
It's not very easy to do a skit by yourself. Sure, it's possible, but it's a lot more enjoyable when you work with a partner. It lets you work with someone else's ideas and gives you both a chance to get more creative. One of the first rules in improvisation is never say "no." This isn't to be taken literally, of course, but it means that as an actor, you should never close off possibilities in the skit. For example, if your scene partner asks "Why are you always at my grandmother's house?" you would not want to deny having been there. It's a great opportunity for you to either give a good one-liner and get back to the scene, or to take the scene in a different direction if you feel it's falling flat.
Maybe you like grandma. Maybe you're trying to get in the will or maybe grandma's a cougar and she's showing you some excessive hospitality. Notice that these are alternatives that seem pretty obvious. That's because they are most often what come to mind. It's important to remember, though, that what's funniest is usually what's least expected. So, say you are trying to get in grandma's will. This is a point at which you would use the mundane to create something extraordinary. What could you want from grandma that would be shocking or change the focus?
This is not to say that you should keep a skit going just to make it weird and twisted. It's best to keep it succinct. Everyone is familiar with the old saying about leaving them wanting more. Well, if there seems to be an endless supply, this isn't going to happen. Many times, when you're on stage, it will be difficult to determine when a skit should end. This is especially true if you are working with a partner with whom you are unfamiliar. If you don't know each other's styles well, then it's good to agree ahead of time to end the skit with a joke that gets a really big laugh. It's very tempting as a beginner to end the skit by killing everyone off so you go out in a blaze of glory or create a sense of finality if not completion. In a short skit, it's not necessary to complete a story arc. Your goal is to make people laugh. They may not care what happens to your characters after the fact, but if they do, then great! It gives you some characters to develop in other situations.Creating a good improv takes practice. It is better to know your partners and learn to think on your feet to create unique situations. No matter what, don't be lazy. It takes a lot of effort, thought, and energy to have a good improvisational skit. Avoid the obvious, and you'll be ahead of most amateurs from the start.
Tips & Warnings
No matter how hard you work, some improvisations will fail. It may be the audience, it may be the timing, it may not even make sense that no one laughed. The important thing to remember is that the more you work at it, the less frequent the failures will be. And the more fun you have doing it, the more fun the audience will have with you.