Tread lightly. It's important to trust the community to second deletions where they are appropriate, or roll them back where they are not. It's an imperfect process, and much of dubious value will be saved from the oblivion it deserves, but it's better than making the decision individually. When we do that, we take away from the community the ability to oversee our actions.
When considering deleting:
[Guidelines originally drafted by KeithBraithwaite at the suggestion of RichardDrake]