One of the few exercises I can do at work. I keep a 60lb DB, 70lb DB and 80lb DB on my boodkself (you should see the gouges! I'm sure my law firm will make me pay for it some day). I do them one-armed, usually three sets:
26 X 60
17 X 70
11 X 80
The form isn't perfect and the reps are admittedly too high, but being able to do a couple sets during work time makes it beneficial for me from a time perspective.
Okay, to respond to the question, I swing the DB (again one armed) to shoulder level, as if doing a curl. Then I press upwards using the other arm to help raise it to full extension (I don't count this as a rep). Then I slowly lower it with one arm. Then, I start the set. After so many reps, when the form starts getting too bad, I stop, so as to avoid injury.