Although this shouldn't necessarily be a hardcore rule, I think this is a much needed "suggestion" that should be somewhere in the rules.
People should search the forums a little before they start posting. I know this is hard without a search feature but even looking at the first page of a category could prove helpful and reduce a lot of the clutter on the site.
There's so many duplicate topics out there (especially in the support sections). I don't know how many times I've gotten "windows crashes when i look at my videos" threads. Seriously a lot of the topics are almost word for word the same. And I usually end up giving the same word for word answer.
Now I don't mind helping people but I think in the long run it's only more beneficial to the person posting, and me, if they just do a little searching before starting a new topic. They find their answer quicker and it saves me some time.
Now I know it's already suggested in some of the Help Sections, but adding it to the official rules might make it noticed more...