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Well, Your question is great. Twitter is important site on google eye, so it's so easily to make your profile at the top on google. From my experience, if you want to get your profile on page one is use your main important keyword with low competition. Example, if your keyword is Paleo Diet, maybe you can take username like (a)paleodietmenus (but I'm afraid this keyword is so difficult to get page one) So, just use your brain. se low competition keyword as your username Good luck
Unique username is the way to go. ALSO, just as important, it needs to be something that can't be "autocorrected" into a different name. For example searching for "blackbooks" gives different results than searching for "black books", so you need to make sure google doesn't see your username as a few words that need spaces between them.
I've read somewhere that some search engines do not understand underscores ( _ ) and that it is way better to use hyphens ( - )
Also, all caps help when searing a username. Uniqueness is a big reason for top of page google results.
There is one way, that you make such posts that people would retweet it, or like it so much that the google crawlers would come to see about your page. And if they would find it legit then your page would be under their radar. Which is good and bad at the same time. But to get people to like your posts or to retweet them, you can use social exchange websites which help you to get those in a few days.