There really is no way to tell you how to get an op-up as it's a mystery to many of us here who have received them. Let's say economy is full and they need more seats. Well if there are empty seats in First/Business they will move passengers up from Economy to free up seats. How they choose I don't know. In over 4+ years flying with United I've received one op-up in 400K BIS miles with UA and it was on my first international flight on UA. I received it in HKG on HKG-NRT. I checked in at the ITCI and received a Business class (upgraded from Economy with a SWU) Boarding Pass as I has expected. Although when I got to the gate in HKG, they had already had a FC boarding pass for me HKG-NRT. I was a 1K and I'm sure there are others who paid more for their ticket than I did. IIRC correctly I paid about $620 for my ticket SFO-HKG-NRT-SFO with a "W" fare basis.