Many new users take some time to get used to Stack Exchange community.
As a consequence we get a lot of "not an answer" answers.
It is very likely that these new users will only seek for guidance after they receive feedback from their first "not an answer" post.
What if the Your Answer box header had a customized messages for <10 rep users? Like below:
The message inside the brackets is just one example, but could be improved to be the most informative as possible, maybe also directing to the help center page.
After reaching a certain reputation threshold (like a privilege), the warning message would disappear.