I used to think American upgrades were a total mystery until my flight from DFW last month. Basically, they use a "pecking order" based on your status level. I’m just a Gold member, so I usually end up on the waitlist. The best way to track your progress is through the AA app—it shows your rank in real-time. If you aren't elite, you can still get lucky with "load factor" offers (cash/miles) that pop up in your reservation. It really comes down to status, fare class, and how many Loyalty Points you’ve banked lately!