I do gaming videos and I plan out ahead about 2 weeks. I figure out how long it takes to an episode and then I see how many videos I can do on the subject. Once that is figured out, I go in and start thinking of my next game.
Example: My current series is Pokemon Stadium. Both play modes (Gym Leader Castle and Stadium Mode) will take about 18 videos considering I put a series intro video out. I know that at my pace of one video a day, I have just over a half a month of videos to play, record, edit, and upload. I already have my next series thought of (Pokemon Red) so I know around video 15 to start announcing it. As for that one, i could easily get 35 parts so I know I have a month or so of gameplay in it.
I don't really have scripts but I have some things that I do for every video now. I welcome everyone early, I ask some questions early and then some more throughout. I just talk about anything that I feel and I leave it open for my audience, I end asking for a like or sub. I really don't know if this is good yet or not because my viewership has been low but I hope to see as my views increase per video.