Well, depending on what slipper type you have (one with a spring or one with conical washers facing each other as a spring), it varies.
With a normal spring type, tighten until spring is fully compressed, then back off 1/4-1/2 turn.
With a conical washer type, you have to be more careful because once you crush the washers, you have no spring left. So, you tighten the nut until the parts are all snug, then maybe 1/8th turn past and adjust from there.
To test, I get my engine warmed up and running well, then I hold the truck down hard with my foot so it can't move and punch the gas. If it takes very minimal throttle for the slipper to slip (less than 1/2 throttle), I tighten it. Usually a quick full throttle pull should break the slipper loose, but you have to be careful. Too much slippage causes heat and glazing. Once your pads are glazed, they will slip a lot easier and get worse very quickly causing excess slip again.