Well, the algorithms RankBrain uses are a bit shrouded in mystery yet, but, concluding the info available here and there, it seems that it may soon have a great impact on how you`d optimize.

I personally find the following prediction to be the most intriguing (and the most realistic): some say that RankBrain will start reverse-engineering the search results; this basically means that Google`s AI might take the search results that seem to do great with users (the ones with high click- /low bounce-rates) for any specific query or topic, and analyze the characteristics such queries have in common, and then use it to evaluate the other pages.

This is just a brief summary, but supposedly, this may have quite an impact on SEO tactics, as this will make the basic common factors like number of links and keyword density a bit obsolete. Such a smart and constantly learning technology may get really hard to trick, still I think the main tactic would stay the same - trying to 'think as RankBrain': analyze the winning results closely and comprehensively to find these common traits Google finds useful and worth bringing up.