I don't know whether Redmine would support this - but would it be possible to show some instructions first when the user clicks "New issue", before the corresponding form opens? While digging through tons of old open tickets, I found that about 70% of them were completely unnecessary, and just a few words first might have prevented them to be issued in the first place.
Something like the text at the end of this mail might reduce the amount of freshly opened tickets.
I'm not sure if redmine supports this directly, but also, our redmine is super old and customized in a way that doesn't work on newer redmine versions, so we're a bit stuck. I put things like this in the FAQ, but that's not very in-their-face of course.
I can say that when we used TRAC years and years ago, we did have something like this in the workflow of the new issue thing and people still didn't read it. So, yeah.... :/
--Dan