Effective Writing
One of the most important guidelines for effective writing that I have ever seen is to know your audience. A lot of people take the attitude that more formal is better. Other people take the opposite attitude: the more like speech your writing is, the more effective it will be. In reality, neither of these is the case. Although writing instructors often have students write formal essays, this is not because the essay is necessarily the most effective writing for every situation. It is simply that, if you are called on to argue a point, being able to write formally is crucial.
Similarly, if you're writing a blog, you need to be able to write in a style that is at once informal and informative. This is in some ways a more difficult style of effective writing because you need to make often intricate points in plain, clear English. Writing effectively is rarely a process of finding the most beautiful ornamentation any two bit hack can do that. Instead, the best writers try to find those few images that will really hit, while cutting out any other decorative nonsense that might get in the way of communicating the message.
Along with knowing your audience, you have to know your genre. Try entering a few writing contests if you don't believe me. Your beautiful, evocative, poetic language won't get you anywhere in a short essay contest. Similarly, your analytical explanations will probably not make for a prize-winning poem. Neither strategy will work well for a short story, which needs to be tightly woven and combine informal speech with more artistic and formal description. You get the idea effective writing depends entirely on what you are working on.
That is not to say that there aren't certain universals in the writing process. Because of the importance of writing in our culture, a lot of people have studied what differentiates well-thought-out, effective writing from poorly written tripe. One of the most important universals is to pay attention to your grammar, punctuation, and spelling. Unless you have some really particular reason to flaunt the rules for example you're trying to emulate some particular dialect or speech style you want to punctuate accurately at all times.
Otherwise, people might look at your writing and dismiss it out of hand, believing it to be uneducated. You may have perfectly good things to say in a very artistic style, but few people will be able to see past the trivial mistakes that you were too lazy to correct the first time around. This is particularly important in business writing, but it is also crucial in academic writing and even fiction to some degree. Never break the rules of writing without reason.