If you are on a successful pro-gaming team you will do well for the most part and will have a easier time of gathering a audience. The other group of people I've noticed that do will on twitch and make decent money are people who are able to entertain their viewers by simply being interesting and/or funny with their commentary as broadcasters. I know of one guy there (Dan whose channel is Dan's Gaming) who earns about 60 thousand dollars a year and all he does is play video games (PC and console games) 8-12 hours a day. He isn't a pro-gamer or anything major but the guy is just interesting to watch and he knows how to have a conversation with his audience even while playing.
I believe most of his money is generated via subscribers to his channel (he has raffles to give away PS4's and other prizes, where the longer you stay subscribed the more tickets you earn for the raffle), ad revenue and donations. He typically gets around 2.5k-3.5k viewers on average everyday. He last I heard had about 1800 subscribers and growing. However it did take him about 5 years to get to the point where he had enough subscribers, viewers generating ad revenue, and donations to basically quit his job and do twitch broadcasting as a full time profession. Additionally it also helps that he lives in a area were the cost of living is relatively low so he can and does stretch out his money to get the most bang for his buck. Yet this guy and others are not the norms as most broadcasters on twitch really don't have enough subscribers to warrant twitch allowing them to have a subscription model for their channel.
I watched a bit of Dan's channel. His channel seems pretty cool, and I can see why it's popular. It might seem that he has an awesome job, but what about the negatives?
-eyestrain from looking at the monitor/TV screen for so long. I went thru 2 eye operations because I was on the computer for long periods.
-obesity from inactivity. Sitting on your butt and playing video games for 8-12 hours a day is not healthy.
-burnout. Everything in moderation. I love chocolate but if I am eating it everyday it starts to lose its appeal very quickly.
-isolation. Yes, he is talking to people in his chat room, but there is no face to face contact.
-arthritis. Playing for a long time can lead to carpal tunnel syndrome. Imagine doing it daily for long periods. I can only imagine what his fingers must feel like after 12 hours of gaming.
Anyway, Dan still has a pretty cool job.