I was facing the same situation when I needed to create an demo video for an app I designed. I had never done any type of video production before. Luckily I found this course on Udemy that lays out all the steps needed to create a demo video http://bit.ly/1bUkHSV

I was then able to go step by step from brainstorming ideas, creating a script, finding artwork, finding music and effects and then optimizing for the web.

Hope this helps.