The best way to do this is with the crank arms installed. Grab the end of the arms and shake. If you can feel play in the axle it's time to tighten up the adjustable cup. Keep tightening and shaking until any play goes away and the axle still turns freely. This is definitely a trial and error process. Hubs and headsets are exactly the same, except the way you test the headset is to apply both brakes and rock back and forth on the handle bars, and with wheels/hubs you grab the rims and rock the wheel until there is no appreciable play. In all cases there will be a point of adjusting a bearing cup (or cone, or race) where the play goes away, but the operation remains smooth. Any tightness, grittyness, binding, or "non-smoothness" means that you need to back off. After you do a few you will learn to have a feel for the process and often get it done in one shot.

What sydney said, but in more detail ;-) He's a minimalist ;-)