I almost never bother with a "flag" unless something is either blatantly illegal or the person posting has shown a total disregard to the value of the community.

Usually, I'll comment on copyright abuse, comment spamming, and shitposts. I won't outright say "Don't do this" and I'll never be insulting or mean. My comment is pretty much always structured in a positive way with suggestions for creating material of great value that will help the poster become a valuable part of our community.

I will also point them at any one of many blog posts I've written about abuse, and creating value in response to the flood of low quality crap. These posts were my way of helping other minnows (and the community in general) begin to become a stream of quality content.