Well my friend charm can only get you so far...first off if you wanna get bumped to 1st class or business class a couple of things will have to happen:
1. The airline has over booked the flight and offer you a later flight with the upgrade
2. You are well dressed,(No Cargo's) and you happen to strike the fancy of the person behind the counter
3. You pay for it
4. You have made a complaint to the airline about a previous flight, and they would like to keep your business
5. Your just very lucky...
6. You have commended the airline for a job well done and they would like to show their appreciation for you taking the time to write.
I have tried to flirt my way into first class, bribe my way into first class, and sneak my way into first class..and in the end, the only way I could pull it off was to pay for it!
No on the other hand, my new brother in law has flown from London to Toronto 26 times in the last 2 years and he has been bumped by British Airways about 15 times...So another factor would be which airline your dealing with.