If you have a good idea for improving the game, that's great, but it's only half the battle. There is still the task of getting the community/developers to understand the idea and agree that it is a good one. Here are some guidelines to help you best deliver your suggestion:
Familiarise yourself with any previous discussion
Do a quick search to see if there are existing threads with similar ideas, and make certain your idea hasn't been shot down before with good reason. You can borrow from past suggestions to improve your own thread or bump them if they haven't played out yet.
Give your idea a meaningful title
Give threads clear titles so people know what they are before entering them. Vague titles serve little purpose in attracting attention to your idea and make it more difficult for others to find your thread when Searching. If a thread inspires a new idea only loosely related to the initial post, start a new thread to prevent the idea from becoming lost.
Avoid making 'potpourri'
Linked to the above, please avoid making grab bag threads with multiple unrelated suggestions. Give each idea its own thread so posters can discuss its merits, so that ideas aren't overshadowed by more popular ideas, and so that they might be found later using the search tool.
Consider and address any flaws of your idea
Please give your suggestions some thought and actual effort. One-liners are less likely to persuade others unless they are an obvious improvement. Consider reasons your idea might not be accepted by the developers. When you do this, occasionally you will realize that the idea should be discarded as unsuitable - but mostly it's just helpful to anticipate objections so that you can address them in your pitch and improve the suggestion. "How might this possibly be exploited?" "Are these changes entertaining or tedious?" "Have the developers mentioned any future changes that would make this idea obsolete and not worth the time to implement?"
Use clear language
This is an international forum where many of the regulars don't speak English as their first language - we don't expect perfect spelling and grammar. However, a good way to instantly alienate about half of your readers is to use shorthand ("u shld make walls more tuff"). Using words that are too flowery, using slang or odd spellings also make your post harder to understand.
Please be as concise as possible when making suggestions. The goal is to have the reader understand your post and agree with it. If they have difficulty understanding your post, find it too long or too annoying to read, they're much less likely to support your idea.
Other notes...
Please be civil when making suggestions if you wish to be taken seriously.
Avoid realism-based arguments and needless complexity - simplicity and gameplay will trump realism every time.
Before you post have a quick reread. Is there anything that could be made clearer or less wordy? Have you assumed people know what you mean at any point?