That's easy. Doing all activities which gives you powerfull stuff with one char. Then switch to 2nd char, get highpower stuff from open world vendors with world materials (this week you get highpower stuff from Devrim Key, Sloan, Asher Mir and Banshee). Then do all activities for powerfull stuff with this char. Switching to 3rd char and do the same thing you did with 2nd char (raise gear at open world vendors and doing activities for powerfull stuff). This all can be raised by doing pinnacle activities with each char.

yeah I was doing all that, I didn't know about open world vendors having high power gear though. very cool.