What do you think that the photograph submission guidelines should be (and why)?

[rpadam]

There has been a lot of (possibly overdue) discussion recently about the type and quality of photographs submitted to the site, so let's see if we can reach a consensus?

If you agree that this would be useful, may I suggest:
a) positive suggestions (i.e. what is good) particularly welcome,
b) no names when discussing what's not so good, and
c) explain why you think something is good or bad, avoiding subjective terms.

NB - I'll hold my hand up and say that I've submitted some poor photographs in my time (particularly those taken on my 'phone, rather than with my camera, at night-time) and have no doubt have approved some pictures outside of whatever guidelines we may agree on, so I'm not trying to claim that I always get things right.