Rule number one. A ringtone knows no irony.
Being born on the trailing edge of Generation X, it's hard for me to accept that anything can be without irony, but the ringtone is the inevitable exception. It's funny to you and your mates, of course. It's the Superman theme, right? Because Steve, mild-mannered accountant transforms int... Well, see how far into that explanation you get on the train, with thirty people staring at you including the girl who, ten seconds ago, seemed quite receptive to being chatted up.
Your ringtone isn't just for you, you see. It's part of your persona. It's what you wear. Except even the loudest shirts don't broadcast their owner's taste quite as far.
Rule number two. That dance number? The one that's been rattling round your head ever since last night at the club? Give it up. You're sober now, and your four-tone polyphonic beeping can't quite capture the same mood as that 50,000 Watt sound system.
In the modern age of polyphonic ringtones, everyone who hears your mobile ring and recognises a non-standard tune is going to be thinking "He paid for that."
My preference is to pick something that sounds like it's a phone ringing, not a Casiotone throwback.
The default tones are safest, the ones that come packaged with the phone, except that every phone has precisely one (1) default tone that doesn't sound like arse. The Sony Ericsson T610, for example, has one halfway-decent tone that sounds like an old-fashioned mechanical phone. Unfortunately, since everyone in Sydney has the same bloody phone, it's inevitable that eventually you'll have to share space with someone who made the same choice, and jump every time his phone rings.
Rule number three. There is a special circle of Hell reserved for people who, on buying a new phone, cycle through every single available tone on the bus or train on the way home.