As a suggestion who comments in threads
1) Do not tell people to post in Megathreads when they come up with a specific suggestion. Megathreads are the book equivalents of "reference books" and "Encyclapedias".
2) Do not link people to other threads that are "In the same general area" but aren't the same suggestion.
3) Mods are not a replacement for any suggestion. Do not bring it up except accompanied by "While you are waiting for this to be implemented, here is a mod that does this". Do not forget these words, they will smoothe out a lot of arguments.
4) Remember that to the person who makes the thread they believe in their own suggestion and are sharing it with hopes of improving the game. Be honest, but don't rip into them.
5) Alternatives and building on other suggestions are far more valuable then saying a suggestion is bad. If it is possible, think of ways it could be implemented.
As for people who make threads
1) Always properly name your thread. The main topic and the specific topic for example "Mounts: Saddles providing a riding bonus"
2) If you have multiple topics that are too numerous to list. Pick the best suggestion in your list and make that as the title with a "+ Other suggestions". OR find a common thread between them.
3) Always search first before posting, as well as the dev list.
4) Stay away from vague "Do better" suggestions. Suggestions need to be specific. "Combat needs to be more interesting" is vague, what could make combat more interesting?
5) Try not to include fixing bugs as a suggestion. Certainly they need to be fixed, but they aren't really a feature.
6) People won't like your suggestions, it will just happen. People will pick on small details or dislike it for fairly asinine reasons. This doesn't mean your suggestion wasn't good.
7) Avoid complaints as suggestions as well. "Dragons aren't fun" isn't specific, do you want them improved, removed, what about them needs to be improved and why?