Write a script for your video podcast. There is no specific required length, but it should be a detailed account of everything that will be said in your vodcast. If you planning to do an interview, all of the questions you will ask should be written out in the script, as well as the introduction & conclusion to the vodcast ("Hi, welcome to Technology Today, I'm Joe Schmoe. In this episode, we will be talking to John Doe about...) You get the idea. A non-interview podcast ("Ask a Ninja", "French Maid TV") should be completely scripted (including any voice-over or narration).
However, when you go to film your podcast, you need not follow the script verbatim; you should allow for a certain amount of improvisation, and editing on-the-fly. If it's obvious that something doesn't work, you are allowed (in fact expected) to change it. The script is not set in stone, rather, it is a starting point, so that you're not trying to figure out what to say once the cameras are turned on ("um...ah...what should I talk about...?").
Type up your script in Word (or InDesign) and give me a copy next week. I want a printed copy and the digital (Word, InDesign) file (which you can email to me).