I made a post about this kinda thing not too long ago, and I'm really happy you're making them. My suggestion in the other thread was for some really short tutorials (probably < 2 minutes). These would be really cool to show on stream during breaks or between games or something. Here were a few ideas that might work in a short format:
-Rollouts (don't need to go super in depth, just show sticky placement if it's demo, and just show the rollout for soldier, and maybe show it twice, from different angles or something)
-Rollouts other than the ones to mid. Some people don't realize there are super efficient jumps to take you from a forward spawn to wherever the fight is. For example, some scouts might not know how quickly you can get onto the other team's battlements from badlands forward spawn (mid->balconey->diagonal->dropdown).
-Tutorial on how to double-bomb soldiers at mid (maybe just show a few frag clips of this working, and have a voice-over of someone explaining why it can be effective, and how your soldiers need to comm that they are doing it, whether it's saying "I'm jumping in 3", or "we bomb when the clock hits :45", etc)
-Explain how crit heals work (such an important thing, and so easy for a newbie to be unaware of)
-Show some quick scenarios where an offclass can be particularly effective (i.e. pyro holding badlands or gully last, or heavy on granary last)
-Building uber (talk about how uber builds faster at certain health, and how the different uber guns charge at different speeds compared to eachother, and compared to building vs. not building)
Those are all the ones I can think of at the moment. I just think it'd be really useful for people who are just getting in to comp. I'm sure there are a lot that watch a stream for the first time and have no idea what's going on, or how/why somebody is doing something, and these could be really quick clips we throw into our comp streams that could help a lot with some of the little things.