I'm going to widen the perspective a little, seeing as a similar-but-not-quite-question just popped up on another board:
For me, the first priority is trust. So, the first thing I do is make clear to the players that they have control over whether their characters live or die (that 6-harm clock plus debilities goes a long, long way), that I do not have a story planned out but I am interested in seeing their characters and seeing them shine, and that I'm going to be transparent with them. Being completely open with information is a part of that, asking provocative questions and building on the answers is a good way of doing that. Such as "Hey Hardholder, if you found the Quarantine's hoard of pre-apocalypse wonders, how would you spend that?" "Savvyhead, how is that anti-brainer gear going?" and so on.
First and foremost, this communicates to the players that I'm a fan of their characters, and that I want us to play to find out what happens. I'm not going to play gotcha or adapt the GM role of providing adversary or obstacles to all their initiatives. I want to see them do awesome stuff!
Second of all, this communicates to the players that they can mess with another player and it can be a gift to that player, an offer to build on. Like, we're going to play to find out what happens, yeah? The important thing is not what you figure out, but what you do with it. The important thing is not if you win or lose, but what you do with it. Your character can be awesome and interesting as a winner and also awesome and interesting as a loser.
Once you got the trust foundation down, once it's clear that the players and the MC is a team and not a rivalry, you can start playing hardball with each other, setting up ambushes and fucking each other over. And keeping secrets and being delighted in being set up by these secrets, if you want. We do it all transparent, though.
This game I went through expectations on the game, a sort of contract before playing. I asked the players what they think we should consider as our goal for our roleplaying, what is good roleplaying, and through discussion we settled on:
* Keep the tempo flowing, be accepting and curious in what is dealt to you and go with it
* Yes-and other players' contributions and build on them
* Try to make all your contributions as offers to other players to yes-and and build on
* Play boldly according to your characters ambitions, don't hold back
What a great gift/offer from my players! This communicated very clearly to me that the players where interested in playing their characters ambitions truly, even when they clashed, and to let these ambitions clash with each other. And it communicated clearly to the players that this is okay, and that we're in this together. This was something we decided together. That's trust.
One thing I'm thinking about trying this game is asking the players straight up "How do you think this fight will end?" if two characters get into a fight, and then go straight to just that happening, no rolls. To really build a sense that they are in control of the story, that I am not going to try to "get" anyone of them but to be fair and to be fan.
So build trust, and remember: Trust isn't built by words, but with actions. Don't just tell the players to trust you, instead start trusting them.