Talk!

Just talk your mouth off, seriously. It's the best tip I can give you to make it interactive.

You gonna open a file and do something, say it, don't just do it. When you are thinking of a problem, ask for suggestions from the crowd/viewers...

Also, ProTip. Vim is a problem if you navigate really quickly along splits (like you should), people lose focus and will just stop following.

I switched to Atom for my last stream (I hate every minute of it) but it slows me down enough so people can follow better.

Hope this helps