I wrote a question, and it got down voted. I'm not arguing, or upset, but I would like to understand what I did wrong, so that I will write better questions in the future (and increase their chance of getting answered). Is it a legitimate question for meta, to post a link to a question and ask for constructive criticism? Also, are there other ways to get some proof reading/advice/mentoring etc?
I would say yes, this is an appropriate use of meta, so long as you focus on how to make your questions more on point.
We also have a chat where you can float rough questions around to other users of the site prior to asking them on the main site.