In response to weematt's query on another thread, thought I'd try to have a go at answering his question about guidelines for Left Alert subs.
I'm no expert, but I believe it's pretty much any format that you could find in a newspaper, but doesn't fit the main news story bracket.
I've had 3 Left Alerts, a spoof job advert, a readers' letters type and the Cameron/Samantha Brick parody piece.
I imagine there would be room for other styles such as horoscopes, reviews, adverts etc. But if anybody can give a more definitive answer then please do. I've enjoyed writing the ones I've done recently as they gave me a chance to write in a different style.