I’ve watched some Jazza videos though mostly ones where he is messing around rather than any tutorial stuff. If you want to do character design then most are humanoid-ish so I’d recommend looking in to how to draw people and proportions. The one book that always gets recommended for that is Andrew Loomis - Figure drawing for all it’s worth. Loomis has other books for specific things too but that one covers general drawing, proportions, size etc.
The other thing that can help is draw every day. It doesn’t have to be for long, detailed or very good but getting in to sketching something every day is a great way to learn, practice and come up with new ideas.
🤣 I’m a jack of all trades, there’s lots of things I can do alright but very few things I do well. I just like to learn new things all the time, keeps things interesting. So currently learning to 3d model in Blender then I’ll need to learn to make textures. I’m following a tutorial for it at the moment but it’s a massively long tutorial so will be some time before I can post any results.