Choose a Video.
The first thing you want to do when making a funny parody is to choose a good video. You will want to choose a video that can be interpreted in many different ways, that way your unique view on how you want to make it funny will be new and exciting to the viewer. Also, sometimes you can automatically see how funny a video can be if you tweaked one part of it and made it hilarious. Sometimes small changes can be the funniest.
Change The Theme.
Now you want to change the theme of the video. You can start by changing the title of the video. An example would be changing "Harry Potter and The Sorcerers Stone" to "Harry Pothead and the Stoned Sorcerer" The title is funny and it can open the gate to a bunch of different ideas on how to make the video.
Write An Outline.
Kind of like a script, the outline will be the basis for the parody, Use the outline to insert jokes, humorous situations and any other ideas you want to add.
Get Friends.
Have your friends join in on your project. Parodies are the funniest when they seem legitimate. The more people, the more "epic" potential the video will have, and the more funny it will be.
Record The Video And Edit.
Record the video and edit it using some video editing software. Vegas Pro, Or Final Cut Pro are good programs but if you are on a budget, you can use Windows Movie Maker if you have a PC, or iMovie if you have a Mac. Editing plays are big part in a video being funny. A search of Weird Al Yankovic will pull up results of great models for editing.