Yes, in ONE there is a great psych force, and this lays out the fundamentals of what is trying to be achieved, there is also a psych force in D+Ms book Irreversible (1st edition, no longer available but the overall effect is included in Identity), there is also a psych force I published in Identity that is, even I will say, a little blatant. If you can get your hands on a copy of Derren Brown's Pure Effect, or buy his video "The Devil's Picturebook" you can get a good start at just what psych forces are. If you have the advocate you can failsafe it.
Oh and a few things, and these really are key--
you're going to practice a lot, and you're going to fail. I'm sorry, that's just how it works in the beginning, then, all of a sudden, when it doesn't seem like you are doing anything different, it will get closer, but still fall short, and then eventually you'll just nail them, you pick up a lot on what is working, how you are suggesting things by physicality, double talk, and changes in tonality, you need to give directions - but you have to spend a lot of time with these spectators beforehand so that you may build strong rapport with them, and when you do other tricks, observe how well they follow your directions. It's also good to preface the force with statements to the extent of "don't think of your favourite card or just a random card, in fact don't TRY to think of anything, if you do, this won't work, I need you to just genuinely keep a blank mind, one will come to you" as an insurance policy, the more of handle you have on how to manipulate and suggest and control, the less you'll have to rely on the latter. Hope that helps.
-Chris