Jump ship to uplevel (E6) preparation tips?

Started as new grad, took 2 years to get promoted to SDE2 (E4) and it was a lot of paperwork (from the technical point of view I was ready a year earlier). So I learned my lesson and for the senior level I simply jumped into another ship at 4 yoe, instead of sweating it to get internal promotion.
I'm at 6 yoe now and I want to get to E6 and based on my experience so far promotion is a less attractive option than external uplevel offers. (TC, preparation, politics, etc.)
I want to know from people who got externally hired as E6 into Fb/G: how hard was it? (It wasn't that hard for E5) what should I prepare (aside from actual experience of building and leading large scale e2e systems and people skills)
Ideally I want to do it over the next year, so want to get some pointers for preparation.
Thank you