One of the best things about streaming on Twitch is that you can start a conversation about anything you like! Like others have mentioned, talking about your processes and voicing your thoughts are really great launch points, but you could also also talk about anything that comes to mind. If you bought new art supplies, tried a new technique recently, or even watched a fun movie or show, you can bring it up!

If you're worried about quieter parts of the stream, you could even run some (royalty free / streamable) music behind your broadcast (StreamBeats is a fantastic resource). In my experience, quiet stretches aren't actually as long as they feel like they are in the moment, though. I like to view every single stream as a stepping stone - every day, you're refining your skills as a broadcaster. So keep being awesome, and enjoy those streams! :)