Michael,
There are lots of theories about how free upgrades are determined by the cruise lines, and the real truth, in my opinion, is that nobody really knows. Having said that, your best chance for an upgrade probably requires two factors to come into play simultaneously:
1. The Sky Suites are totally sold out and there are requests from customers / TAs for more.
2. The higher category suites are not sold out, and closer to sailing Celebrity judges that they
will sail empty.
Whalla, they upgrade you and get an additional Sky Suite sale which they presumbably wouldn't have had. There are plenty of people who believe that being a member of the Captain's Club helps. Others
believe another factor is the frequency of your sailing with them. I think that there is more luck involved than science.
Good luck and enjoy your cruise.
Ted