you can add your affiliate link under your profile picture .or send a twitter infomation of your affiliate link
2.using youtube to promote?
Yes youtube is very effective tool to promote , you can add your affiliate under your video you upload and add some desicption . and at mainpage of your youtube channel you can also add your affiliate link on it ,its approved to be more effecive to bring sales.
3. what other social media to recommend
I think they are facebook ,instagrame ,tumblr . which is very important ,you can do the things like the twitter ,put your affiliate link at the mainpage that is the most recommended.
you have other questions
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