Also check to see the flight numbers are correct on the waitlist. I found out the hard way this morning.

I cleared for an upgrade on my return (LHR to SFO) 12/5, but wondered why I had not cleared for my outbound (SFO to LHR) tomorrow 12/1. Found when I made the reservation, the CSR waitlisted my upgrade for the wrong flight (956 instead of 954).

From now on I will personally double check the flight numbers to make sure I am waitisted for the correct flight.