Question: Mine is simple. I up vote any answer I think will be of value to the OP and to others with a similar problem. If I think the answer will only be of use to the OP (this usually stems from the question being very localized), I will up vote the answer when the answer takes a broad view of the question and goes sufficiently beyond the local needs of the OP to have archival value. I always feel sad when such an answer is lost because the question gets closed.

To be fair to all who answer a question, my policy requires me to revisit a question whenever a new answer has been added to up vote again if another worthy answer has been added. I accept this responsibility.

I'm pretty sure some others have different policies. I don't claim mine is best. In fact, I suspect it might be too simplistic. I'd like to see other policies expressed. One might be so much better than mine that I will replace my current policy with it.

Do you have a different policy? If so please write it up as an answer.

### Edit

I already discussed my criterion for rating a question as good in [this answer](https://mathematica.meta.stackexchange.com/a/1308/3066) to Mr.Wizard's question. That set my ***question*** up-voting policy because a good question is worth an up vote.

Answer: 
I don't really have a firm "policy" - I have a tendency towards indecisiveness and I'd spend far too much time pondering whether or not an answer met my criteria (and whether or not my criteria needed revising!).

So I vote fast and often, without overthinking it. If I read an answer and think "yeah, good answer", I upvote. It might be good because I learnt something, or because it contains a great explanation of a tricky concept, or a lot of time and effort went into it, or just because it includes some nice elegant bit of code.
This is a Q & A page. 

When I need answers to specific questions, I search with keywords and usually find fair questions but even better answers. If a Q / A element solves my question or brings me a good bit closer to the solution I rate also old solutions positive.

I do upvote "old" responses. 

One time "Questioner" I ignore. 

A good question is well written, well researched and reduced to the minimum, a "minimal working example" in the proper sense. Such questions are interesting because they show that the questioner is interested on his level of an answer. Such questions I upvote.