We've got lots of existing meta posts about how many bad questions there are and how much of a problem they are (or aren't) - that's not what this question is about.

I wanted to collect in one post some techniques for finding bad questions and dealing with them and it should come as no surprise that by "dealing with them" I mean to downvote the bad ones.

The automatic delete rules are our friend here: questions with no answers and negative scores (or 0, or even +1 in some situations) will be automatically deleted if they meet certain criteria. I'll be posting some of the searches I do to find bad questions and anyone else who has ideas can do the same.

Here are the automatic deletion rules:

9 Days

If a question was closed more than 9 days ago, and ...

• was not closed as a duplicate
• has a score of 0 or less
• is not locked
• has no answers with a score > 0
• has no accepted answer
• has no pending reopen votes
• has not been edited in the past 9 days

... it will be automatically deleted. This check is run every day.

30 Days

If a question (open or closed) is more than 30 days old, and ...

• has −1 or lower score
• has no answers
• is not locked

...or if it was closed and migrated to a different site...

... it will be automatically deleted. This check is run every week. (0300 UTC on Saturday, to be precise.)

1 Year

If a question (open or closed) is more than 365 days old, and ...

• has a score of 0 or a score of 1 with a deleted owner
• has no answers
• is not locked
• has a viewcount <= the age of the question in days times 1.5
• has 1 or 0 comments

... it will be automatically deleted. This check is also run once a week.

Duplicates

I am awaiting clarification on what happens with questions closed as being duplicates. From what I've seen, duplicates are treated exactly the same as any other question under the 30- and 365-day rules: they're gone. But OTOH, I've seen comments (including from SF mods) that duplicates don't get deleted, and I've seen lots of comments on meta.SO that they don't and/or shouldn't get deleted.

References:

1. The official FAQ post on meta.SO about how deleting works. The first answers includes the rules for automatic deletion, and links to more detailed explanations given in the next reference.

2. The post on meta.SO that most clearly states when "bad" posts are automatically deleted. This includes a new rule for automatic deletion that was added in June 2013.

3. Since the automatic delete rules mention locked questions, here's the official FAQ post on those.