Firstly, know what to watch. Don't just go in with nothing ready, especially if you want to watch movies. Square it all away BEFORE you start, which is crucial if you need to upload the video first.
Secondly, get your CyTube ready. Preload the video into it and just watch for a little bit to make sure it's compatible and nothing is broken. Read the documentation for CyTube and understand the moderation tools (also remember to give yourself Leader), understand the special commands like /d for drinking games and /say for special messages, and maybe think about adding some cool/funny/useful emoticon images. Also, set the permissions for who can add videos, where they can add them (next or at the end of the playlist) and everything else.
Then, make a topic when you're ready and make sure it's appealing.
