MSNBC.com and Forbes.com gives us some tips how:
Resist Outright Bargains
The class of ticket you buy often determines the likelihood of an upgrade. Travelers who buy full-fare coach seats have a better chance at getting into first class than those who choose discounted seats, which often aren’t upgradeable. It’s easiest to find and reserve full fares by talking with a telephone agent directly or using an airline’s online booking system where classes of fares are clearly marked.
I think I’ll stick to buying discounted fares and crossing my fingers, wishing somebody wants to change seats with me. I would love to experience flying first class someday; right now it pains me to look at first class ticket prices. Besides, flying economy is a big part of the aventure, isn’t it? 😉