My policy is simple too: Try to act, always. It is important that this doesn't automatically means an up-vote. It includes down-votes, close-votes, reopen-votes or comments. The idea behind this is simple, if I take the time click on a post to read a question, I have already spend some of my time. Usually, I do this because I find the question interesting or I see that I probably can answer it easily. Anyway, in my opinion, leaving this page without any action, will turn our community into an ignorant crowd I see so often on other SE sites.
My specific policy is the following:
When I answer a question, I up-vote the question in 90% of the time. There are corner cases, but in general a question which interests me enough that I write an answer, deserves an up-vote from me. The most annoying posts are, where people have written several answers (with up-votes) and the question has only one or two up-votes. Look at this post: 6 answers, 17 up-votes in total and no one voted for the question? Either the question is really bad, then it deserves to be down-voted or closed, or it is a valid question another beginner probably will stumble upon sooner or later, then there should be at least some up-votes.
If a question has many answers, I try to read through all of them and give an up-vote to each that has value for later visitors in it. Sometimes, I start reading from the bottom, just to see whether the current order of answers is really due to quality or due to other SE effects like fastest gun in the west. In my opinion the difference of votes between answers is often not fair. Take for instance this post, where I gave the accepted answer. Don't you think that the other answer deserves some more up-votes and the the difference of currently 9 votes is only because many people just up-vote the answer at the top? What if I tell you that @librik works for Wolfram and has an awesome knowledge about low-level I/O? Go ahead, read his answer (and maybe look over another one of his posts) and then come back and rate the quality of the information he has given again.
If a question is not well formatted or lacks of important information, then I usually vote to close and comment. If I think the question has no value whatsoever, then I additionally down-vote, because questions with a score of -4 or lower are no longer shown on the main-page. In the case of answers, I down-vote only if the answer contains wrong information or it really doesn't add any value to the issue. This case is really rare.
Finally, I don't think that everyone's specific policy is that important. It is fundamentally important that you vote. Otherwise, and here I'm pretty sure, our main site will soon look like the main site of this community and this is not what we have worked our asses off to get this site going.
