Here are some steps to practice in preparing to learn to write your own funny jokes and one liners.
Listen to a lot of jokes.
Listen to, read, tell and examine a lot of jokes. Pay special attention to your favorite kind of joke as these may be the very kind you end up writing. Like any other writing, you have to be very familiar with the territory you are operating in before you attempt to add something worthwhile to it. Once you are in constant touch with jokes and general humor it will be easy for you to see what type of thinking and design goes into crafting a funny joke.
Start small and work your way up.
First, unless you are very fortunate, expect to write a lot of bad jokes before you write any good ones. Like with any new venture, or any new genre of writing, you will look like you don’t know what you are doing until you do. You may want to keep the first 100 jokes to yourself or share them only with those who will be very kind if your gag flops.
Second, you may want to start small by writing one liners first and then graduating up to longer jokes and then stories. The simpler ideas and constructions may come more quickly and with this success you’ll have a foundation to build on.
Some specifics about construction.
Make the punch line, the point where it all comes together, something unexpected. If it is a surprise and it is funny but true and also somewhat of a logical ending, you will be in the ballpark of where you need to be to get lucky once in a while and write a truly funny piece.
Spark people’s curiosity. The more involved people are in your plot, the more likely when they do laugh that they will give themselves fully to that as well.
Make sure you construct the whole thing from commonly known bits of information. If you tell them the one about the fuel for rocket formula that was missing some ingredient and this is all only funny to those who understand rocket science, you will have shut your audience out, and maybe even insulted them.
Write jokes that are a takeoff or extension on something another writer or comedian has been successful with. Try your own version of something others have heard but be sure to make it funnier and worth hearing again or it may backfire.
Twisting things around. Today, twisted humor is very popular. Be just plain silly, goofy and ridiculous in what you are writing and you have half the battle won.
On the other hand, it may work for you to create a hilarious side bender that sounds serious to the last moment then turns into a riot. When such a joke is written it is often intended to be told with a completely straight face; this approach has worked for many joke writers when matching the right material to the look and presentation of a good “straight man”.