If you try to blag an upgrade it's also worth making sure you have the right appearance, airlines don't want dreadlocked hippies with facial piercings lowering the tone of their business class cabins. If you can, try to look the part with the following:
Smart conservative clothing (no ripped jeans or belly hanging out)
Tidy hair (not multi coloured spikey hair)
No facial piercings
No visible tattoos
And always ask politely, you won't get anywhere by being agressive or demanding
