That's the main question you should be asking yourself whenever you put pen to paper (or fingers to keyboard as the case may be).
The reason this question should constantly be on your mind is that for your audience to understand what you're saying you've got to have a pretty good idea yourself.
Whether you're writing a blog post or a quick email you need to always be aware of the point you're trying to get across (which in this case is making you aware of the point you're trying to get across) and avoid rambling on and becoming confusing.
Don't start writing until you know EXACTLY what you want to impart to your audience and you'll notice that writing on the whole becomes a lot easier, and what you do write is a lot clearer and to the point.
Staff Training explores effective written communication in its Business Writing workshop. Follow the link for more information or email info@stafftraining.co.za