Originally Posted by
golfingboy
Book your ticket and make sure your Mileage Plan # is in your reservation... The system will automatically add you to the upgrade waitlist

If you log in first before making the reservation and then your number will be added to your reservation automatically.
And if for some reason you do forget to do this, you should be able to pull up your itinerary online and click a link that says "Request Mileage Plan Complimentary Upgrade" or call the MVP desk and have them waitlist you.
I second the welcome to FlyerTalk!