I added a list of acknowledgements at the end so people could see what tutorials and software I used to create them, but very basically the steps I take are:
1. Use the inbuilt STO demorecord feature to record segments of gameplay.
2. Use demorecord to playback the gameplay, and use its camera sweeps.
3. Use fraps to record the playback to video files.
4. Import the video files into Windows Live Movie Maker to organise and trim them (and add soundtrack).
5. Upload to YouTube.