Step one: place a generous layer of grease in both (inner/outer) races. There's no need to use grease sparingly: be generous.
Step two: stick the balls in the grease. Now comes the question: should you reuse the old balls instead of replacing them for fresh ones? Technically speaking a used ball bearing looses its shape and gets ovalized through normal use. Common wisdom would advise to replace them. I, on my hand, carefully examine them once cleansed and if they look right I reuse them. Anyway this time -and for no special reason- decided on new balls. I had to visit three hardware stores and overcome the clerk's incredulity ("Sorry Sir but I don't thing there are bearings that small") For three euros I stepped out with my precious tiny ball bearings. (Yes, they actually had them.)
Now the grease should hold the bearings in place provided you are not interested in acrobatics such as throwing the pedal in the air or something
Stick as many ball bearings as there's room for but always leave room for one more. That allows the balls to run freely on the race.
Remember my speculation about a missing ball in the outer race?. Well, it doesn't hold water now. I placed thirteen balls on this race just to find later that the pedals were not spinning smoothly. Took one ball off and... Voila! Smooth as silk.
Step three: carefully slide the axle into the pedal's body. There's no need to grease it up. It'll get properly lubed while passing through the inner's race "generous" layer of grease.
Step four: Screw the adjusting cone gently with your fingers. No tool needed here. Stop when you feel you have reached the ball bearings. Do not overthigten in fact don't even tighten it , just stop when you feel you've reached the ball's surface. Then slide the washer (align the lip to the slot, remember) and screw the adjusting hex nut. Tighten it with the fingers.
Step five: check adjustments. If everything has gone right the pedal should:
a) run smoothly as silk
b) show no side-to-side movement (hold the axle end with one hand and try to pull in-and-out the pedal's body)
If the pedal is not running smoothly unscrew the hex-nut and the cone a bit and recheck. If the pedal's too loose unscrew the hex-nut and thighen a bit the cone.
Repeat this double checking till you feel satisfied. If so hold the axle with the 15 mm wrench and use an 11 mm wrench to tighten the hex-nut. Now, remember to re-check the spin (some times you are not aware of your own strength!)
Step six: screw in the dust cap (make sure it won't come loose) , remove the excess of grease. and you're all set!