You need to brainstorm upon the ideas or themes on which the videos will be based upon. You need to find something interesting and easily accessible on the internet. However, something that is difficult to be found will also make the contest a lot more interesting because you will also learn from it. The research of individuals will help you to know different aspects of the topic that were not known to you before.
You need to go through state laws to understand the requirements for launching such an event. You probably will need to hire a lawyer who will assist you in letting you know the possible themes that are prohibited in your state etc.
You will have to look out for sponsors who will be willing to pay for the cost of hosting an event and also the gift hampers or anything that will be distributed amongst the participants and the audience. It is crucial to get a big company name that will not back-off at the last moment because in these tough financial conditions finding a sponsor is difficult.
You will have to find a location where the exhibition of videos or the event will take place. You can hire an expo centre but it may cost you a lot so you can always go out for an open-air setting where the cost of hosting an event is much less.
Determine the guidelines that you want the participants to follow and place all the competition related information along with the participation guidelines at your website. Promote the event through free mediums like facebook etc.
Judge the videos on the day of competition and thank everyone for their efforts and time.