I just got a reminder (while upvoting an answer) that I hadn't upvoted a question in a while.
As it turned out, I had explicitly chosen to go to that particular question with the intent of upvoting the question (because I was already aware that I hadn't done so in a while and was looking for a question I felt worthy of an upvote). Nevertheless, that shows that the reminder was 'reminding' me appropriately - it had been long enough that I already knew it was true.
To be honest, I don't think I upvote a high enough proportion of questions.
My overall record is fine (about as many questions as answers have been upvoted; I think several answers upvoted for every question would be okay), but I seem to be finding it much harder to upvote questions lately.
When I read an answer, it's easy to find reasons to upvote; some good, helpful points that address the question (or important aspects of it), no major errors, and I am happy to vote up... and when I really don't think I can upvote, I can make suggestions that would make the answer better and perhaps upvote later. Indeed, I sometimes find it hard to wait until I have finished reading a well put answer before I upvote.
When reading questions, however, I don't very often feel like I am reading a good question. I don't so often think a question satisfies "shows research effort, is useful and clear".
Generally it seems like there's some problem that makes me hesitate - the question has pretty much been asked already, or the poster hasn't really thought about what they want to ask - indeed, likely hasn't even googled their question or checked Wikipedia. Maybe it's a question that wouldn't be widely useful, or (oh, so often) the poster hasn't even bothered with basics like layout or spelling. [Not everyone can spell, but computers are pretty good at it; as I type this question, I get a little wiggly red underline under misspelled words, which I assume is my (pretty standard) browser checking what I type -- it doesn't like upvote, googled and wikipedia above; the last I have now capitalized.] It is sometimes worse, like when people can't even bother to spell a word wrong the same way twice in a row.
Perhaps my standards for questions are too high, or perhaps I am missing some other opportunity to upvote questions.
The only thing that occurs to me is to be more diligent about coming back and upvoting questions that the OP is willing to improve. That doesn't seem like it would increase my upvote rate enough.
If one - or quite often, 3 or 4 - of our diligent editors makes a poor question into something approaching a decent question, giving reputation to the original poster for someone else's work (often needing a lot more effort than the original took) seems misplaced.
What are some good reasons to upvote a question? When might I think about upvoting?