I came across this article with a great tip for get a flight upgrade with miles. I tried it the other day and it worked! Here’s how it works:
We have never bought an upper-class seat; if ever we’ve flown anywhere up front, we’ve used miles to upgrade from economy. If you want to do that, call reservations and drop the name “revenue management.” The reason is that revenue management’s job is to make sure a flight is profitable, so they’re the ones telling [reservation agents] what they can say; they’re like Flying Club’s boss. Not everyone knows that this department exists, and by mentioning it you reveal yourself as someone who knows how things work and understands how seats are released. Say to the agent: ‘Have revenue management released any first-class seats for miles upgrades yet?’ When they say no, ask them to check or just be put through to revenue management so you can ask when they will release some, as well as how many seats are left. Politely respond like this: ‘You have 20 seats unsold? Why aren’t you releasing them?’ Often by the end of the conversation they say, ‘OK, we’ll release one for you,’ or they might tell you to call back tomorrow. Doing that, we’ve had a pretty much 100 percent success rate.
The rest of the article has other random travel tips. Check it out here if you want to see more: https://www.bloomberg.com/news/articles/2018-02-21/the-two-words-that-will-help-get-an-airline-upgrade-over-the-phone