If JFK is your airport, I would suggest first and last flight out of the day for upgrade. Last flight (41) to SFO is best because there are no connections in SFO at Midnight to AS. One way to read the tea leaves to see what AS wants for a discount first class ticket. The lower the price, the best chance for an upgrade. Best fares seem to occur 4 to 6 weeks before departure. Buy one way tickets for maximum flexibility.