No such thing unless you have the status or major luck - they may roll oversold Coach folks up one notch the next class of service, but unless they are desperate that will generally apply to people with status first.

Definitely do not believe any old rubbish about dressing appropriately or asking nicely - it's just that, rubbish. If you want to fly better on AA, read the FAQ and appropriate parts of the Wiki, become informed and then put the knowledge to work.