Depending on which airline you're flying with,you may or may not get that elusive upgrade.
Some carriers(i.e. the one I work for)are more than happy to put their own staff in business or first,whilst letting other staff slum it in economy.
Others will put you in business/first willy nilly.
Apart from dressing smart,if you really can't hack it in economy,try and get predicted loads for the flight you want by contacting the airline.If it's chocca in economy but empty in other classes,an upgrade could well be coming your way!
Having said that,staff travel is not the perk it once was,and as echoed in the previous post,I now find myself just happy to be on the flight even if it means 10hrs in a jumpseat.