Well first of all it's all about networking and scheduling. I've yet to officially start but I've done some experiences on my personal channel/twitter.
Follow brands and companies that relate to you. I've barely opened my twitter and already have 20 people following me. Other gamers and streamers. Hopefully these are people I can reach out to in the future for collabs and the likes.
Learn how to hashtag. Use about 1-2 hashtags per twitter post. Any more and it's annoying.
Schedule your posts. It will make your life SO much easier.
Google calendar can also help with that! I have everything planned out on mine.
Copy pasting is troublesome. Post to all your social networks at the same time when you'll be streaming.
Consider getting a youtube channel and bringing in traffic from there. Make some compilations of fun times on your stream and upload them to youtube.
These are the top social networks that you should assure you have:
Twitter Facebook Instagram Snapchat
(Post to these anytime you go live!)
Optional:
Tumblr (this is mostly because I don't like the drama much, tumblr all in all is great for reaching out.) Ask.fm (It's nice to have a place where people can ask you questions without feeling overwhelmed. A lot of people are shy. Some a dicks yeah, but a lot of them are shy.)
Hope that helps a bit! Good luck!