Watch a bunch of other streams, SR and Dominion, and right down what you like they do and what you wish they did.
Offering insight and analysis on what you are doing, what you did wrong, and what others did wrong is probably the best way to have a quality stream.
It takes a level of awareness to be able to tell if you yourself made mistakes and what they specifically are. I suggest to get in this habit by first using LoLRecorder and watching your own matches over and critiquing your play out loud.