The secret is, there is no secret. Just conversate with them like you'd conversate with any other person you'd conversate with who you don't know very well, like your hairdresser for example, but keep her laughing, so make it light-hearted conversation. Literally your only job is to make them think "this guy seems alright" so when you do make the move and ask them if they wanna stay out tonight or whatever, they think why not, because they see you as a safe pair of hands.
If you're crap at keeping a conversation going generally, then maybe improve on that before you go on the pull, watch some YouTube vids or whatever. Plenty of "getting to know you" questions you can ask, though, like how old they are, what they do for work and so on.